hello ade001, please go through the steps described in [[How to fix preferences that won't save]], they should hopefully contain a fix for this issue.

Try to delete the compatibility.ini file in the Firefox profile folder. You can use this button to go to the Firefox profile folder: *Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder) *http://kb.mozillazine.org/Profile_folder_-_Firefox ---- It is possible that there is a problem with the file(s) that store the extensions registry. Delete the extensions.* files (e.g. extensions.sqlite, extensions.ini) and compatibility.ini in the Firefox profile folder to reset the extensions registry. *https://support.mozilla.org/kb/Profiles New files will be created when required. See "Corrupt extension files": *http://kb.mozillazine.org/Unable_to_install_themes_or_extensions *https://support.mozilla.org/kb/Unable+to+install+add-ons If you see disabled or not compatible extensions in "Firefox/Tools > Add-ons > Extensions" then click the Tools button at the left end side of the Search Bar to check if there is a compatibility update available. If this hasn't helped then also delete the addons.sqlite file.