The latest stable build of Firefox – version 9, for those not up to speed with Mozilla's rapid-fire release schedule – is readily awaiting your download (Windows | Mac | Linux). The update comes just over a month after the release of Firefox 8 and the first beta of Firefox 9. Despite the relatively brief development cycle, Mozilla has crammed plenty of changes into December's revision.
The largest change appears to be the addition of Type Interface, which reportedly improves JavaScript performance by 20-30%. It remains to be seen how that translates to real world performance, but every millisecond counts. ExtremeTech tested a pre-release build of Firefox 9 this summer and recorded notable gains in Kraken, V8, Fishbowl and other benches with Type Interface enabled.
Folks updating from Firefox 8 can also expect support for querying Do Not Track status via JavaScript, font-stretch (a CSS property), better text-overflow support as well as improved theme integration for OS X Lion. Apple's operating system also receives two-finger swipe navigation, though we're not entirely sure what this entails. Firefox 9 also touts improved support for HTML5, MathML and CSS, as well as the obligatory bug fixes, which are too numerous to list here.
Given Mozilla's hasty development cycle, Firefox 10 and 11 are already available in alpha forms and we wouldn't be surprised if the former reached beta before the end of 2011. We don't see anything particularly exciting about the next stable build, but it should fix an annoying bug that causes the back and forward buttons to stop working when visiting Google+. WebGL gains anti-aliasing and the forward button will be hidden until you navigate back. More details here.