After releasing the first beta version of Firefox 4 about three weeks ago, Mozilla have a new beta build ready for release. This new release packs over a dozen new features and is actually considered safe for day to day browsing tasks despite being a beta build.

The latest release brings the Mac OS X UI up to date with the Windows version – with all the tabs on top and new CSS3 goodness. Performance and startup time have also been improved significantly thanks to a rework on the XPCOM module. Scrolling and CSS3 animation performance would also see a boost thanks to a new Retained Layers system which can render and then cache the entire page in memory making it unnecessary to repaint everything on every refresh.

App Tabs now also make an appearance in the Firefox 4 Beta 2 build. You can right click on any open tab and “Make it into an App Tab” – which are like the Pined Tabs in Google Chrome. Javascript engine has also been optimized for further speed boosts, though I couldn’t test it yet on the SunSpider benchmark. There are over 650 changes from the previous beta build in total.

I couldn’t get the Acid3 score on Firefox 4 Beta 2, because AcidTests.org was down at the time of writing. I’ll update the post with benchmark performance stats and the Acid3 score as soon as I can test that.

For now you can download Firefox 4 Beta 2 for Windows, Mac OS X, and Linux by following the link in the download box below.