Hello,

This happens in safe mode?

• Firefox in safe mode

Try go to your profile folder, maybe you need unhide the hidden files and folders, close firefox, and rename or delete the localstore.rdf file:

• http://kb.mozillazine.org/Show_hidden_files_and_folders
• Profiles

Then restart Firefox

Make sure that you do not run Firefox in full screen mode (press F11 or Fn + F11 to toggle; Mac: Command+Shift+F).

• https://support.mozilla.org/kb/how-to-use-full-screen

You can also check for problems with preferences.

Delete a possible user.js file and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release.

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