I am using Windows Vista. The last thing I saw was the Firekeeper Plugin update and Firefox stopped working after the last release of Firekeeper. It was beta anyway.
There is also an Application event if you look at the event viewer complaining about the Firekeeper plugin.
You need to uninstall Firekeeper but how. I have tried to delete the two Firekeeper.dll from
C:\Users\<your-user>\AppData\Roaming\Mozilla\Firefox\Profiles\2ezme861.default\extensions\firekeeper@mozdev.org\components
and
C:\Users\<your-user>\AppData\Roaming\Mozilla\Firefox\Profiles\2ezme861.default\extensions\firekeeper@mozdev.org-trash\components
But I couldn't because of an unknown permission problem. I am not using UAC and I am an SA on the system and permissions look alright to delete these folders.
The only way was to restore the previous version of this folder by right clicking on the folder and select Previous Versions tab.
I thought I have turned off this feature because it was costly but here you go. It saved the day. Firefox is running normal now. I should wait till the Firekeeper released to production.