Lot of problems or errors occurs when starting a Browser can be caused mainly due to corrupted profile or some problematic files in Firefox user profile also lead to prevent Firefox from starting and shows errors this can be fixed by deleting secmob.ini and compatibility.ini files from profile folder manually, ProfileCleaner extension for Firefox allows to automatically delete these files when Firefox exits.
Instead of removing the problematic files mentioned above from Firefox profile each time before running Firefox, you can use ProfileCleaner Firefox add-on as an alternative which automatically deletes problematic files from Firefox user profile when Firefox exits.
User need to select compatibility.ini and secmob.db entries in the ProfileCleaner preferences to let ProfileCleaner delete these files automatically on exit so that these errors will be fixed on next Firefox startup.
So use this extension only if you have Firefox startup issues that can be fixed by removing secmob.db and Compatibility.ini files from Firefox profile.
I have Firefox 16.0 and it says that ProfileCleaner is not compatible with that version. Are you planning on an update to make it compatible? Thanks.
FYI I am not the developer of that add-on.