Google announced yesterday that as of the beginning of August they will no longer provide support for the even slightly out of date web browsers, so you'll need to update your browser to one of its 2 latest versions. For example, there's a Firefox 4, 3.6, and 3.5. The latter will no longer work with Google Apps, even though it's barely 2 years old.
Basically Google have decided that they don't want to support conservative users anymore. If you're like me, and you are cautious about upgrading critical apps like your browser, Google's new decision might exclude you as a user.
Take Firefox 3.5 and Firefox 4, which came out in June 2009 and March 2010, respectively. I still regret upgrading to FF4 in late 2010; I've seen significant drops in performance and stability as well as a noticeable increase in its demand for system resources. (And then there are the unnecessary changes to the interface, which I still think are ugly.)
But on the plus side, this probably won't affect most users. it only applies to Google Apps, which is a specific subset of Google services. Unless I misunderstood the announcement, the regular Google services (gDocs, gmail, etc) should be unaffected.