An anonymous reader writes "Last week we heard complaints from Mozilla that Windows RT would restrict users' choice in web browsers, unfairly favoring Internet Explorer over alternatives like Firefox and Chrome. Unfortunately for Microsoft, the situation is now on the Senate Judiciary Committee's radar, and they will look into claims that Microsoft is engaging in anti-competitive behavior. That said, it could be a difficult case to make, since Windows RT is destined for ARM-based tablets, and Apple currently dominates that market. 'When it comes to proving abuse of monopoly power, an important question is determining the market in which a monopolist has power — the relevant market, in antitrust legal terms. In the [late '90s] DOJ case, U.S. District Judge Thomas Penfield Jackson's findings of fact concluded Microsoft had a monopoly in the market for "Intel-compatible PC operating systems." Windows on ARM doesn't run on x86 chips, so by Jackson's standards, Windows RT hasn't been judged to be part of Microsoft's monopoly.' Microsoft addressed some of these issues in a blog post in February."