Windows Defender Finally Squashes Firefox Bug That Ate CPUs For 5 Years (pcworld.com) 85
An anonymous reader shares a report: Firefox has a reputation of being something of a resource hog, even among modern browsers. But it might not be entirely earned, because it looks like a CPU bug affecting Firefox users on Windows was actually the fault of Windows Defender. The latest update to the ubiquitous security tool addresses the issue, and should result in measurably lower CPU usage for the Windows version of Firefox. According to Mozilla senior software engineer Yannis Juglaret, the culprit was MsMpEng.exe, which you might recognize from your Task Manager. It handles the Real-Time protection feature that monitors web activity for malicious threats.
The bug was causing Firefox to call on the service much more frequently than comparable browsers like Chrome or Edge, resulting in notable CPU spikes. Said CPU spikes could reduce performance in other applications or affect a laptop's battery life. The issue was first reported on Mozilla's bug tracker system way back in 2018 and quickly assigned to the MsMpEng service, but some more recent and diligent documentation on the part of Juglaret resulted in more swift action from Microsoft's developers.
The bug was causing Firefox to call on the service much more frequently than comparable browsers like Chrome or Edge, resulting in notable CPU spikes. Said CPU spikes could reduce performance in other applications or affect a laptop's battery life. The issue was first reported on Mozilla's bug tracker system way back in 2018 and quickly assigned to the MsMpEng service, but some more recent and diligent documentation on the part of Juglaret resulted in more swift action from Microsoft's developers.
Resource Hog? (Score:5, Insightful)
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Modern web browsers in general are resource hogs. They are projects on at least the same level of complexity as the OS they run on. The newest release of Firefox might be marginally better than the newest release of Chrome (idk, I haven't done benchmarks), but both certainly rank among the most resource-hungry programs your computer runs on a regular basis.
It's plugins (Score:2)
And yeah, it wouldn't surprise me in the slightest if this was on purpose, but even if it wasn't I doubt they went out of their way to fix it.
Re:It's plugins (Score:5, Informative)
Yes; Microsoft's actually a rather huge factor in this. The code shipped by Firefox does not call upon this service at all. It calls the kernel's VirtualProtect() function often - which has to do with applying properties to pages in Protected memory. Windows Defender was injecting excessive, unreasonably wasteful computations hampering performance; a correction reuslts in a Five-fold performance increase for Firefox. See Bugzilla 1441918 [mozilla.org]:
This performance issue makes calls to VirtualProtect (among other things) unreasonably expensive on Windows platforms when Windows Defender's Real-time Protection feature is active (the unreasonably expensive computations execute in the MsMpEng.exe process).
On Firefox's side, independently from the issue mentioned above, we should not consider that calls to VirtualProtect are cheap. We should look for opportunities to group multiple calls to VirtualProtect together, if possible. Even after the performance issue will be mitigated, each call to VirtualProtect will still trigger some amount of computation in MsMpEng.exe (or third-party AV software); the computation will just be more reasonably expensive.
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DOS ain't done 'till Lotus won't run!
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Re:It's plugins (Score:5, Informative)
It always had a reputation for memory leaks, even without plugins. It's my one major criticism of Firefox since they changed to single-number versioning, pretty much every version since 4 has been a memory hog and just eats memory in the background if you leave it idle enough.
2.x and 3.x were nothing like as bad as 4, and recent Firefoxes (last 2-3 years) have been absolutely abysmal - 16Gb if you have a handful of tabs open. WTF?
If you're seeing issues like that, it's a problem with the addons you have. I regularly have dozens of windows open with lots of tabs in each, and it never goes over a few GB used. And I usually leaving it running for weeks at a time.
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What part of "even without plugins." did you skip??
I also used FF 2.x and 3.x without plugins for years and it WAS a memory hog. I tended to leave my computer on for months at a time and FF would slowly suck up RAM. The only way to fix it was to completely shut down and restart FF.
It was a known issue that was ignored for years by the FF devs.
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Kindly go fuck yourself and let the adults in the room continue the discussion about the OPs discussing the history of FF -- both early and current.
I used Netscape Navigator before switching to FF 2.x. It would constantly eat RAM. I ran ZERO plugins. One time it was hung so I attached a debugger to it and was able to get it unhung so I could save my tabs. I ran FF 2.x for years.
When FF 3.x came out I switched to that. I ran ZERO plugins. Same issue as CONSTANTLY eating RAM.
When FF 4.x came out I switched
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What part of "even without plugins." did you skip??
The part where you're having a problem that is unique to you and widely known to be related to plugins. We read what you wrote, we're assuming you don't have a clue how to use your computer and thus probably have plugins or other trash in your user profile that you're unaware of.
Backup your bookmarks and reset your Firefox profile. You broke something. Mozilla went out of their way to recognise that most of these issues are user related and even provide a method for you to reset to a clean state. Help >
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Ah, the armchair "expert" who "magically" knows what a stranger experienced even though they never met. Let's blame the victim for FF's bugs. /s
I learnt 6502 assembly when I was 10, learnt x86 assembly, wrote a few TSRs for MS-DOS 5.0, and back in the early 2000's attached a debugger to FF 2.x when it was hung and was able to get it unstuck long enough to save all my tabs. But riiiight, I don't know how to use a computer and MUST have installed plugins because obviously "you were there". /s
I never used FF
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Re: It's plugins (Score:2)
Sounds like just another of many issues in their code base. For many years they had a handle leak related to images that eventually consumed so many handles that it would cause a BSOD on Windows 2000 and later OSes. Of course the Mozilla developers scoffed that it couldnâ(TM)t be their fault and that no real operating system could be brought down by an applicationâ(TM)s behaviour. In this recent case, Iâ(TM)m wondering what other browsers were doing differently to avoid the problem and why
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According to the bug report, Chromium was calling the function less (batching many operations behind a single call). But it was more than that as Chrome was actually using a DIFFERENT function (VirtualAlloc). It turns out that VirtualAlloc can do the same thing that VirtualProtect does, but it is a lesser known trick so antiviruses don't trigger their protections. And even if they know about the trick, they have less information to work with so they can't scan as much.
See: https://bugzilla.mozilla.org/s.. [mozilla.org]
Re: It's plugins (Score:3)
If you read this ticket, you will see that they just gave up waiting for a response from Microsoft. They knew that Chrome behaved differently five years ago and didnâ(TM)t think think they could optimise FF any better but instead seemed to expect Microsoft to do something. Bad attitude and poor project management.
https://bugzilla.mozilla.org/s... [mozilla.org]
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I can't really blame Mozilla that much. They were using OS functions normally in an intended way and there was no performance problem with the way they called those functions. They tried to get Microsoft's help and attention 6 years ago but they were literally just told to post about it on the Feedback Hub and hope Microsoft even bothered to investigate it. Looking at the ticket, it looks like it took somebody basically reverse engineering Defender to figure out what was going wrong before Microsoft acte
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It will simply gobble up the memory you have doing nothing. It isn't going to fight for resources that are being used. They cache old pages for longer in case of ctrl+shift+T to bring up an old tab and even cached images from days, even weeks ago if you never closed it, etc. The more you memory you have being unused, the more it will go without "garbage collecting"
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Re: Resource Hog? (Score:2)
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Re: Resource Hog? (Score:2, Informative)
Not using available RAM is dumb. It's there to be used. If at any point you are spending CPU cycles to load something that could otherwise be in RAM, something has gone wrong.
Re: Resource Hog? (Score:4, Insightful)
I want RAM available to the next process I want to run, too. There's no reason to get carried away allocating it all. I don't have 32GB so that Firefox can use 31GB
Re: Resource Hog? (Score:2)
I've never in my life ran out of RAM and found the culprit to be Chrome. Maybe Firefox developers just suck at writing performant code.
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I find it ironic to call Firefox a resource hog when chrome routinely uses multiple GB of memory per tab due to "design choices" that the arrogant googlers seem unable to figure out.
The relative differences in memory use between browsers is borderline indistinguishable. The design choice here is that users want their content available (keep it loaded in memory), and the security afforded by per tab process isolation (no memory sharing between tabs). Yes it's wasteful and I'm thankful it exists. I do not pine for the old days where browsers used little memory and yet the entire damn thing crashed or ground to a halt when there was even one misbehaving tab.
Disclaimer: Posted from a compu
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Agreed, especially since Firefox IIRC was originally intended as a lean+mean revamp of Netscape. Today I find it far better-behaved than Chrome.
Thank You (Score:5, Funny)
I won't bother posting that I think it was intentional to keep Firefox performance behind IE and Edge.
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Marc Andreessen: "Netscape will soon reduce Windows to a poorly debugged set of device drivers."
MS are just proving Marc's point for him.
Mozilla dosen't care (Score:4, Insightful)
Re:Mozilla dosen't care (Score:5, Insightful)
So are you saying that Mozilla should have gotten Microsoft to fix the Windows Defender bug sooner, or are you saying that they should have been able to figure out a way to change the Firefox code so as to work around it?
Re:Mozilla dosen't care (Score:5, Insightful)
Reading the nuance, it seems that while Windows Defender make VirtualProtect extra expensive, Firefox suffered disproportionately by calling the function more than the alternative browsers.
So they consider that the Windows Defender was doing something unreasonably over the top inefficient, but it could also be argued that Firefox is being strange calling it so much more than other applications.
So it boils down to why does Firefox call it so much? Is it because it is implementing a protection mechanism that the other browsers are not using? In which case, may be good on firefox. Is it because Firefox makes a lot of little calls rather than aggregating? That would strongly suggest Firefox would want to look toward optimization. Is it because Firefox keeps changing its mind about the protection of a memory range? That would also suggest that perhaps the logic isn't great.
Not as cut and dry as 'Microsoft had this bug that inflicted poor Firefox' and more 'this VirtualProtect thing is more expensive than perhaps the developer thought, and folks in both Microsoft and Firefox have opportunities to mitigate that issue'.
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So it boils down to why does Firefox call it so much? Is it because it is implementing a protection mechanism that the other browsers are not using? In which case, may be good on firefox. Is it because Firefox makes a lot of little calls rather than aggregating?
The way the Firefox team responded to this sounds like it's mostly the former with a little bit of the latter. I really got the vibe that Firefox could have optimized things better, but it wouldn't have made a huge difference until Microsoft fixed their issue.
Re:Mozilla dosen't care (Score:5, Informative)
A lot about the summary is plain wrong. MsMpEng.exe is not your task manager. It's part of Windows Defender. Firefox was not doing something out of the ordinary. It was just allocating memory and releasing memory, which isn't optional if you want to keep memory usage under control as the user opens and closes tabs. Also Firefox wasn't asking Windows Defender to do anything. Windows Defender decided it should inspect what Firefox put in that memory, so it copied it to a temporary file and then did a virus scan of it, which was taking forever. Chrome, Internet Explorer and Edge also do the same type of allocations, but apparently Windows Defender didn't deem their allocations to be worth the same level of scrutiny.
Firefox runs fine on other platforms that don't have this crap going on in the background. In this case it is a Microsoft issue, but as a programmer I can tell you anti-virus software in general causes these sorts of performance degradations all the time. One of surest ways to speed up your PC is to turn anti-virus off, because if effects almost everything. Paste a jpeg into a word document and write it, and a short while large the antivirus software will silently scan the entire file for viruses. It will do this every auto save.
Malware is a problem on todays internet, but anti-virus was the wrong solution. Even when anti virus software is perfectly bug free their patterns regularly miss the occasional virus, and they are silent resource hog. I have no idea why Microsoft persists with it - other OS's like iOS (BSD) and Android (Linux) have other solutions that are far more effective. They sandbox every app, so one gets infected with a virus it can't touch the rest of the system. Nothing can get missed. With anti virus people blame the app they are running for their PC slowing to a crawl (look ma, when it's only slow when I use the app) - when it reality it is the anti-virus screwing soaking up CPU time and disk IO by running their leaky sieves over the same files, over and over again. And that is what was happening this time.
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According to this bug report (1822650) [mozilla.org], it looks like Chrome/Edge was actually using VirtualAlloc instead of VirtualProtect. Apparently VirtualAlloc can do the same thing that VirtualProtect does, except it generates a different (and maybe even misleading) event that causes antiviruses to skip a bunch of checks.
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I have no idea why Microsoft persists with it - other OS's like iOS (BSD) and Android (Linux) have other solutions that are far more effective. They sandbox every app, so one gets infected with a virus it can't touch the rest of the system. Nothing can get missed.
Windows can't do the same thing as iOS and Android, because backward compatibility would suffer, and it is at least 50% of the reason for using Windows in the first place. It would we far better if you had explained how standard Linux avoids malware, because it would be something that Windows could do, without sacrificing so much.
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The summary doesn't actually claim that, although it's badly enough worded that I also thought it did until I reread it because that interpretation was obviously wrong. What it says is
A better wording might be "the culprit was MsMpEng.exe, which might be a name you recognise if you look at Task Manager to see which processes are hogging your CPU".
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A lot about the summary is plain wrong. MsMpEng.exe is not your task manager.
If you're going to criticise the summary it helps to not advertise that you didn't read it correctly in the opening line. The summary does not say MsMpEng.exe is your task manager. In fact it says specifically what it *is*.
Chrome, Internet Explorer and Edge also do the same type of allocations, but apparently Windows Defender didn't deem their allocations to be worth the same level of scrutiny.
Defender doesn't care what the applications are when allocating memory. The fact is Firefox was calling it different. Yeah Defender could be more efficient (evidentially) but Firefox also had the ability to work the same way as the other browsers, and didn't.
There's blame to go around. Le
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other OS's like iOS (BSD) and Android (Linux) have other solutions that are far more effective.
Well, BSD and Linux don't have particularly more innate solutions to the problem, nowadays they generally bank on a more disciplined user base at this point, and relatively lower share as to not be as worthwhile for malware. At one point in history, it was the case that Windows had a privilege problem (Win9x had no meaningful privilege separation, XP had credible privileges, but an ecosystem that induced folks to just run as admin all the time).
Android and iOS do have a tighter security model, by going to
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What the heck are you talking about? (Score:5, Insightful)
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Mozilla didn't squander that lead. They were knocking it out the park. Then Chrome came along and it's kinda hard to compete with Google's money and the fact that every time you "google" something you get offered Chrome. Never mind that Google owns 71% of the global smartphone market.
That might be true for the personal computer/user market, but sadly the personal computer market isn't going to pay the bills of a company releasing a free web browser.
In the business market, Mozilla completely threw their lead out the window by choosing to be actively hostile to business networks.
They dictated the person using the computer must have more rights than the owner of the computer.
Block internal DNS so no connecting to internally named servers.
Not supporting Kerberos authentication.
Block certifi
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and the fact that every time you "google" something you get offered Chrome.
In fairness, that was a very small factor in Chrome's uptake, and by far the least unethical or illegal part of it. It might have been good for a couple of percentage points, but compared to the hijack installs (Google paying to have Chrome bundled with basically everything on Sourceforge at the time), or sabotaging YouTube on every other browser and putting "Try Chrome" popups *there*, it was a drop in the ocean.
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and the fact that every time you "google" something you get offered Chrome.
Most people don't give a shit about the "offer" and Firefox's popularity plunged deep long before Google and Microsoft got into their pop-up tug of war.
Firefox's development was slow and unfocused. For the longest time they seemed to care more about doing irrelevant shit than to fix bugs or address performance issues. I'm glad when they released Quantum a few years back, it was the point where I reinstalled it on my system as I once again considered it "viable". But the damage was done. I moved to Chrome ba
Good progress (Score:1)
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If Firefox is crashing for you, try recreating your profile from scratch.
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This is not a good answer. Firefox needs to be able to detect and fix now outdated config settings that people had to implement because it was doing something wrong or stupid previously, and now they do something wrong with a setting that previously made sense.
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Unfortunately, that was Mozilla's own answer, the "Refresh Profile" feature does exactly that. It creates a new profile, then uses the Import features to give it history, bookmarks, cookies, etc. But it does not import in extensions, or settings for those extensions. You need to export any custom settings from uBlock Origin, uMatrix, any custom userscripts from TamperMonkey, any settings you applied in FrankerFaceZ, etc...
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I'm well aware that it's their official answer, but unfortunately, that doesn't make it good.
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Like Chrome doesn't .... or Edge ... Or Opera ...
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The only other solution to offer a lot less options that can be customized, and ignore any legacy ones.
The downside of offering flexibility to power users is sometimes users can do things that cause problems down the line. There isn't a "crash_often = true" settings anywhere that can be easily removed. If you're having problems, it's because you changed a weird combination of settings that people normally don't touch.
Re: Good progress (Score:1)
It's been fixed for ages (Score:1)
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Firefox crashes at least once every five minutes on my PC and this has persisted through several clean sheet Linux Mint installs. I've figured it was hardware related, but no other programs do this.
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Your PC is a piece of shit. Blaming Firefox just shows your own ignorance. Sorry to be harsh.
Carry on.
Re:It's been fixed for ages (Score:4, Informative)
>"Firefox crashes at least once every five minutes on my PC and this has persisted through several clean sheet Linux Mint installs. I've figured it was hardware related"
It almost certainly is. I have literally *HUNDREDS* of machines running various versions of firefox all day, every day, under several Linux distros (native) and several different hardware platforms and none of them ever crash. I had a friend running Linux with similar problems to yours, and it ONLY affected Firefox. I told him for years it was hardware. He finally replaced the video card and all the problems disappeared.
>"no other programs do this."
See above. It is likely that no other program on your computer runs as much, uses as much CPU or RAM or video, either. In today's world on a typical desktop computer, the browser will be the first to expose hardware issues, by far.
I am running Mint at home. On this AMD machine, Firefox is running 24/7, with dozens of windows and many tabs in each, for weeks on end without any issue.
Meanwhile, another friend running Linux uses Chrom* and complains that after a day he is swapping because it eats all his memory over and over. Chrom* is NOT better than Firefox in overall performance or security, and it DOES use more resources, all while respecting your privacy and open standards less.
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He finally replaced the video card and all the problems disappeared.
That could have still been a driver bug, if literally only Firefox was affected, and he switched to another generation of the hardware. Firefox doesn't put very much strain on your GPU.
Chrom* is NOT better than Firefox in overall performance or security,
Chrome used to be process-per-tab, which arguably was better for security at a substantial cost in memory. Now apparently you have to specify --process-per-tab, and it doesn't necessarily actually do it even then. I'm underwhelmed by the performance myself, though. I did finally get ungoogled-chromium to build (they updated s
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>"but I'd still rather use Firefox. "
Then why wouldn't you?
So .... (Score:3)
The "Bug" in Firefox is a problem with a Windows service ...
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Not quite. The "bug" in Firefox is also related to how Firefox interacts with the Window service. The particular service doesn't treat each application differently yet Firefox was disproportionately affected compared to other browsers.
Car analogy:
You and I have a car. We both drive on roads. You live near the highway and spend all you day driving through the highway except right in front of your house. I spend all day in the suburbs driving through one school zone after another. The government decided to "f
Wait... whose bug? (Score:4)
Wait, so was this a bug in Firefox, or a bug in task manager that disproportionately affected Firefox?
Because the title is clearly laying it at Firefox's feet - but that seems very unlikely. Mainly because it required Microsoft developers to fix it - and there's nothing they can do to fix a bug in Firefox.
So it sounds to me like they fixed a Windows bug, that for some reason was being disproportionately triggered by Firefox.
Re:Wait... whose bug? (Score:4, Insightful)
Basically it seems that Microsoft improved the performance of Windows Defender when an application makes a VirtualProtect() call.
Firefox was disproportionately impacted by the high cost because they called that function way more than others did.
Hence the actual bug concluding: Great, Microsoft improved the performance of that library call, but it's still expensive and Firefox should do things to reduce the number of times it invokes VirtualProtect, like aggregating requests and such.
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Far more likely is Microsoft "fixed" the bug by whitelisting Firefox in Windows Defender, so it doesn't intercept Firefox's VirtualProtect calls.
Users open and closing pages cause browsers to have highly variable memory usage patterns - Google sheets runs an entire spreadsheet in a browser for example, so you are looking at the memory usage of Excel in one tab. And VirtualProtect() doesn't do
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No, Chrome and Edge just use VirtualAlloc, which antiviruses check differently. The problem was that when Defender saw Firefox make a call to VirtualProtect, it tried to parse the ETL event. This parsing function was written poorly and ended up allocating and de-allocating a 64KB zeroed memory block for each of the 18 different event attributes. So every single time Firefox called VirtualProtect, Defender would basically malloc/free a 64KB memory block 18 times. And frequent memory allocations are not c
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Awesome answer. Thanks.
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I might be being unfair here, but I've heard this story from Mozilla many times. Bug is reported but it takes years and years for someone to properly debug it and figure out how to fix the problem.
In this instance it sounds like Microsoft deserves some of the blame, but Mozilla is often frustratingly slow to identify and fix these issues.
Re: Wait... whose bug? (Score:2)
It might have been a Microsoft issue, but why didnâ(TM)t Mozilla devs track down and identify the problem? If they then couldnâ(TM)t get Microsoftâ(TM)s attention, they could have looked at what other browsers were doing or tried to find a work around such as the one suggested above. Itâ(TM)s like they donâ(TM)t care about the user experience or creating a competitive product. Think of all the cycles they wasted on continually reinventing a terrible UI when they could have been f
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task manager
No one said it had anything to do with a task manager other than you may recognise the service running if you looked in task manager.
So it sounds to me like they fixed a Windows bug, that for some reason was being disproportionately triggered by Firefox.
Correct.
Way to twist reality... (Score:2)
SO... in REALITY... it was a BUG in Windows DEFENDER, right?
That BUG in Windows DEFENDER forced FireFox to eat the CPU.
But the bug WAS in Windows DEFENDER.
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Now adobe (Score:2)
Re: Now adobe (Score:2)
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Next up: Fix: SECOMN64 Sound Research SECOCL64 (Score:2)
If the headline reflected the article... (Score:2)
Re:If the headline reflected the article... (Score:5, Insightful)
>"Windows Defender Finally Squashes Windows Defender Bug That Ate CPUs For 5 Years while Firefox was running"
+1
Exactly. And here it is CORRECTLY worded from pcmag.com: https://www.pcmag.com/news/5-y... [pcmag.com]
"5-Year-Old Windows Defender Bug That Caused CPU Spikes on Firefox Finally Fixed" "It took over five years, but Microsoft has finally fixed a bug[...]"
And Techspot:
https://www.techspot.com/news/... [techspot.com]
"Microsoft fixes 5-year-old Windows Defender bug that was killing Firefox performance"
And The Register:
https://www.theregister.com/20... [theregister.com]
"Microsoft deigns to fix five-year-old Defender bug that slowed Firefox [] Windows giant would never try to get an unfair Edge over rival, surely"
And several others. In fact, I could find NONE that were so incorrectly worded as the PC World one. Their article, poorly selected for Slashdot, is CLEARLY slanted unfairly against Firefox. Not just the title, but this gem:
"Firefox has a reputation of being something of a resource hog, even among modern browsers"
Really takes the cake. It most certainly does NOT have any such reputation that I have seen or heard of. In fact, it has a reputation of using LESS resources than Chrom*.
Then the article implies that it is somehow Mozilla's fault that the 2018 bug was not diligently documented enough to get MS to respond. As if MS has much incentive to fix something that mostly seems to affect their Chrom* browser competition. Hmm.
DOS isn't done until ... (Score:2)
That's the first sentence that comes to mind whenever I see any third party program running badly on Windows was found due to a "bug" in Windows.
I guess Firefox is no longer a threat to Microsoft now, so it is ok to "fix" the bug.
Maybe not a bug and not fixed for Windows 7 (Score:2)
Finally (Score:1)
I noticed that my laptop fan would whir loudly while Firefox was active, even if it was "idle" (which is not saying much for a web browser with tens of open tabs). Chrome and Edge would not do this (with the same tabs open) Inspecting Task Manager did not show that it was using excessive CPU time, but if I closed Firefox, the fan would spin down. In order to get peace from the whirring noise, I finally decided to hibernate my laptop when I'm not using it (what a concept. BTW, sleep is no good because Window