When Firefox crashes, it usually records information about what was happening at that moment. You can submit that data to Mozilla and share it with forum volunteers to see whether it points to the solution. Please check the support article "Firefox Crashes" (especially the last section) for steps to get those crash IDs, and then post some of the recent ones here.

Since you also crash in Safe Mode, could you disable the Flash Player plugin's protected mode or, as a quick test, disable the Shockwave Flash plugin for a while.

To disable protected mode, see the steps in this support article from Adobe under the heading "Last Resort": Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?

Note that your System Details List shows that you have a user.js file in the profile folder to initialize some prefs on each start of Firefox.

The user.js file is only present if you or other software has created it, so normally it wouldn't be there. you can check its content with a plain text editor if you didn't create this file yourself.

The user.js file is read each time you start Firefox and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session.

• http://kb.mozillazine.org/Preferences_not_saved

Thanks for your help. It turns out that I was getting infected with the FBI Moneypak virus, source unknown. Little by little other things were not working as usual and then I got the locked out by the FBI screen when rebooting into Win 7. I don't know why the sysmptoms were only apparent in Firefox and not Explorer (web sites not working or crashing the browser), but eventually my machine was completely locked.