Mozilla Delivers Firefox 3.5, Beta 4, and It's Snappy
If you've been contemplating moving to one of the later betas of the new version, Beta 4 definitely seems stable enough to start using. My one complaint with it so far is that my Firefox extensions don't work with it (see the no-go message above), but if extensions are critical to you, you can use Beta 4 for standard browsing, and keep a previous version of the browser around for use with extensions.
As Simon Mackie notes on WebWorkerDaily, in addition to the TraceMonkey-driven performance boosts, Beta 4 has better support for web technologies such as HTML5 and downloadable fonts. If you haven't kept up with downloadable fonts, definitely check out the video interview with Opera's Håkon Wium Lie, found here, on why they're important. Essentially, these can give you access to thousands of slick fonts on the Web, instead of the very limited number found on an average computer.
As Simon notes, many users will also like Firefox's ability to reopen closed tabs and windows in case the browser crashes or you accidentally close something you need access to. To reopen, you just select options under the History menu, as seen above.
Firefox 3.5 Beta 4 is likely to be the last or second-to-last release of the browser before version 3.5 is finalized, at which point every Firefox user is going to want to get it. I wish my extensions worked in Beta 4, but I'm happy enough with the speed to use it as my primary browser and reach for an older Firefox version when I need extensions.
By the way, Linux users of Firefox may want to check out Tux Radar's benchmarks of Beta 4, here.