A speed increase in the JavaScript Tracemonkey engine is probably the most noteworthy change in Firefox 3.6 Alpha 1. A quick test at the Sunspider JavaScript benchmark confirmed that the new alpha version renders the test in about 300ms faster than the latest official release Firefox 3.5.2 (800ms compared to 1100ms).

Other new features include the addition of several CSS3 attributes including background-size, CSS gradients, multiple background images and support for the rem unit from CSS3 values and units. Most add-ons were disabled upon first startup of Firefox 3.6 Alpha 1 with the possibility to force them into compatibility. The Nightly Tester Tools are unfortunately not compatible with this new release which means the easiest way to force add-on compatibility is to disable the compatibility checks.

To do that enter [about:config] in the Firefox address bar and filter for the term [extensions.checkCompatibility]. Double-clicking that value will set it to false which will disable the compatibility checks in Firefox. Interested users can download Firefox 3.6 Alpha 1 for Windows [link], Linux [link] or Apple Mac [link]