Do you still see any extensions in the extensions folder in the Firefox profile folder? You can use this button to go to the current Firefox profile folder: *Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder) *http://kb.mozillazine.org/Profile_folder_-_Firefox ----- Do you have an "Old Firefox Data" folder on the desktop in case you have refreshed Firefox and created a new profile? *https://support.mozilla.org/kb/reset-firefox-easily-fix-most-problems You can recover data from such a saved profile, but be cautious to recover possibly corrupted files. *https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile ----- It is possible that there is a problem with the file(s) that store the extensions registry. Delete the extensions.* files (e.g. extensions.json, 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 menu button/Tools > Add-ons > Extensions" then click the Tools button at the left end of the Search bar to check if there is a compatibility update available. If this hasn't helped then also delete the addons.json file.

Thank you all! I found the add ons manager file.

''FrankMichael [[#answer-807421|said]]'' <blockquote> Thank you all! I found the add ons manager file. </blockquote>