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Add-ons are unable to be activated

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I can't activate add-ons, specially stylish and social fixer. If I activate them and click on restart to activate them, Firefox restarts but they are still deactived. I tried resetting Firefox and even reintalling (both Firefox and the add-ons) but nothing worked.

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Start Firefox in Safe Mode to check if one of the extensions (orange Firefox button, top left corner (new fx menu for v29+)/Tools > Add-ons > Extensions) is causing the problem (switch to the DEFAULT theme: orange Firefox button, top left corner (new fx menu for v29+)/Tools > Add-ons > Appearance).

  • Do not click the Reset button on the Safe mode start window or otherwise make changes.
  • Windows/Mac: Go to Help > Restart with add-ons disabled
  • Linux: Run firefox -safe-mode in the Terminal/Konsole
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You can 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.


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.

New files will be created when required.

See "Corrupt extension files":

If you see disabled or not compatible extensions in "Firefox/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 possible addons.json and addons.sqlite files.


You can use this button to go to the currently used Firefox profile folder:

  • Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)