Firefox 3.7 Alpha 2 will be officially released in the next few days, however, the release schedule does not have the actual date of the release, but you can download Firefox 3.7 Pre Alpha 2 "Minefield" right now from their FTP Repository.
Firefox 3.7 Alpha 2 will come with the 1.9.3 Gecko engine, and also includes new icons and other features which makes Firefox a bit faster than the earlier versions. The Pre-Alpha does have a stable version of separate processes for Plugins which works better than my earlier tests.
However, Firefox 3.7 did fail the Acid3 test and was given a rating of 96/100 as compared to current version of Opera and Google Chrome, which both received 100/100 in the Acid3 tests. Even Firefox 3.6 had a Acid3 rating of 96/100.
If you are a brave-heart and want to test the Pre-Alpha2 of Firefox 3.7, head over to the nightly build repository and download the appropriate version. FF 3.7 Pre-Alpha2 is available for downloads for Mac, Windows and Linux.