Latest Firefox version (updated on 8/21/2010) will not start.
Actually, problem started early on 8/21/2010 - before I upgraded (through IE, since Firefox will not start). When I try to start I see what looks like just the top of a Firefox browser page that seems to be trying to open GMail - which is my standard mail service. However, this appears for less than one second and then all that is visible is the Firefox application icon in the task bar. This icon does not work - I cannot open the window via this icon. I am forced to close the application using the task manager (which, erroneously, does show the application as "Running").
Wšykne wótegrona (1)
You can try to right click that icon on the Task bar and choose Move or Resize to see if that can make the Firefox window visible.
You can also try http://kb.mozillazine.org/Corrupt_localstore.rdf (caution: do not delete the localstore.rdf file in the Firefox program installation folder)
Create a new profile as a test to check if your current profile is causing the problems
See Basic Troubleshooting: Make a new profile
There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins"
If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files)
See http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox