What to do when add-ons don’t install as they should.
Compatibility 
Works with:Firefox 3.6+
Background
For the most part, add-ons (extensions and themes) are trouble free. However, once in a while an add-on will not install, upgrade or uninstall correctly. Or may be you launched a different version of Firefox on the same profile and now your add-ons are disabled because Firefox says they are incompatible. These are most common issues with add-ons Installation:
- Extension(s) not installed after restarting Firefox
- Add-on(s) Disabled by Firefox
- Blocked Extensions
Extension(s) Not Installed After Restarting Firefox
This issue is becoming less common but use to occur frequently with extensions that did not upgrade correctly. There were some extensions that required you to remove them before installing the new version. Failure to do so resulted in a phantom extension that could not be upgraded or removed.
If after restarting Firefox the extension has not installed go to the Tools Menu and select Extensions’ or Add-ons’. The extension appears in the list with this message (Name) will be installed (removed/upgrade) when Firefox restarts.
Add-on(s) Disabled by Firefox
Firefox will automatically disable any extension that is not compatible with build you are running. This will happen if you try to run and older or newer version of Firefox on the same profile. However, even after you return to the correct version of Firefox, it will not automatically re-enable the add-ons for you. The good news is you shouldn’t have to go through and reinstall all your extensions.
The Tweak
- Close Firefox
- Locate your profile folder
- Delete the following files from your profile folder and restart Firefox. Note: You may not have all the files listed below:
-
- extensions.ini
- extensions.cache
- extensions.rdf
- extensions.sqlite
Firefox will rebuild your extensions and themes list and these files. Your extension should be re-enabled and functioning again.
Notes
Firefox 8 introduced new Add-on Install Controls. Before performing the above tweak we recommend users Disable Firefox 8 Add-on Controls before performing the above tweak.
Blocked Extensions
Normally if an extension has been blocked by Mozilla it will automatically be removed from your extensions list on the next Firefox restart. Further, Firefox will display a dialog window advising the extension has been blocked. Trouble is the window can get buried behind others. However in the Firefox Add-ons Manager, the add-on will be showing disabled with a message add-on as been disabled for your protection. Mozilla has a Block List of extensions, plugin and themes.
We do not recommend attempting to bypass this security feature.
Updated: November 15, 2025
