Aware that 4.0.4 will not function properly with win7 completely but the option is there so I decided to try out Firefox 3.5.5. Created a couple packages, one on XP SP2 32-bit and another on Win 7 64-bit and the results have been the same when running the virtualized package on Win 7 64-bit.
When trying to attach a file to a message in gmail for example, when it opens the file dialog window, it crashes. Any pages with Flash content will also crash the browser. Plus it'll crash from time to time for no reason at all (haven'tdone any logging at this time).
I'm sure there are more issues but at least it's something we can experiment with until full support comes later next year.