Installed Firefox 4 Beta 8 on my Windows 7 32 bit machine. Went to the demo page, waited for it to load, hit the start button, and my machine immediately crashed (black screen, no hdd activity, not responsive). Rebooted, tried to load random page from my bookmarks, crashed again. Fortunately that time it didn't take my whole computer with it. Guess I'll try again in a few weeks?