In less than 4 years, Microsoft's Chief software architect Ray Ozzie revealed that they will be moving from "bundled packages" into internet-based functions entirely (Windows Live!), so I suggest not being swayed by current and soon-to-be-unveiled marketing campaigns regarding utilities, OS, or other tools.
The pressure to "upgrade" to IE7, Office 2007, and Vista (even by building in redundancies and traps via the constant barrage of auto-updates on unsuspecting user systems) is completely overshadowed by the impending quantum shift to Vienna (the successor to Vista), scheduled for release in 2009.
This shift by Microsoft from providing "stand-alone" systems to requiring web-based licensing makes a pretty good case for savvy developers to consider migrating to other independent (and more reliable?) utilities and systems, such as your mentioned FireFox browser, ACT for email and information connectivity (rather than Office), and other open source OS (already available and touted as "best of breed").
* Interesting thought: If the industry is moving everything to web-based applications, how soon should we expect the monopoly of ISP's to start raising monthly connection fees through the roof?? Makes a lot more sense to support the Free Net bills moving through Congress even now..... "Preferences" do not usually indicate intelligent progress, but like trends and other variables, constantly change according to opportunity (or so they should!). Source: Optmize Magazine, March 2007 "Update: Is Microsoft in The Groove?" IMO