The newest build is 0.2.0. You can download it here.
What's New In 0.2.0
The latest build of Chimera demonstrates a highly experimental implementation of Quartz rendering. The current build locks you into Quartz, but the Quickdraw renderer will still be available via a pref in a later point release. For now you're locked into Quartz with the current build. Also, printing with Quartz turned on is pretty busted, so don't even bother. :)
Chimera 0.2.0 has much improved scrolling over previous versions. Most importantly it now uses native Aqua scrollbars rather than emulating the look via the Appearance Manager. Scrolling is also much faster, using both the wheel and the keyboard.
The tab browser feature has had some crash fixes and speed enhancements. You can now also cycle through tabs via the keyboard and close tabs. In addition the tab strip will auto-hide when only one tab is being used.
Chimera 0.2.0 has a new splash screen, application icon, and new toolbar and sidebar icons.
Finally and most importantly Chimera has had many crash fixes and stability fixes.
Chimera has complete build instructions on mozilla's Web pages (under the code name ChimChim). You can find those instructions here. Be aware that the downloadable build listed above contains numerous patches to Mozilla that have not yet been accepted, so any builds that you do will not be as stable or as performant as the downloadable build above.
If you have questions about building, use the chimera mailing list or hop on to #mozilla, and someone can help you out.