After upgrading from Firefox 3.6.11 to 3.6.12 on a Windows Vista 32 bit OS Firefox opens with a full screen, about 75% of the screen is a normal window, however the bottom 25% is a second area. The line between the two areas can be dragged to the bottom of the screen, however this must be done every time Firefox is opened. The initial screen is a blank screen.

The profile between the two OS's is shared and has been shared for several years without any problems. This is a multi boot environment so only one copy of Firefox accesses the profile at a time.