This article describes how to uninstall an extension or theme that can't be removed by following the instructions in Disable or remove Add-ons or Remove a toolbar that has taken over your Firefox search or home page.
If you can't access the Add-ons Manager or if the Remove button is grayed out for a certain add-on, you may need to uninstall it from Firefox Safe Mode.
Once Firefox has started in Safe Mode, try removing the add-on again and then restarting Firefox.
Some add-ons are installed by other programs. You may be able to remove the add-on from the Windows Control Panel or Settings page.
Sometimes installing or updating other software will add an extension which can't be removed from within the Firefox Add-ons manager because its Remove button is not functional.
The software that added the Firefox extension may include an option to remove it. You should visit the support site of the software provider for more information. As an alternative, simply disable the extension in the Firefox Add-ons manager if you no longer wish to use it. To disable the extension, select it, then click on its Disable button. The extension will be disabled after you restart Firefox.
If you have programs that use Microsoft .NET Framework components, a Microsoft update may have installed an extension called Microsoft .NET Framework Assistant.
To remove this extension, follow the instructions in Microsoft's article How to remove the .NET Framework Assistant for Firefox.
If you have Java software installed, you may see the Java Quick Starter extension in your list of extensions. This extension has its Remove button disabled.
To remove this extension, follow the instructions to disable the Java Quick Starter in Oracle's Java Quick Starter article. You may need to close Firefox while executing those instructions.
When you restart Firefox, the Java Quick Starter extension will be removed.
If you can't remove an extension from Firefox using the other methods described above, you can manually remove it. First navigate to the folder where extensions are installed:
Open your profile folder:
Click the menu button , click help and select Troubleshooting Information. The Troubleshooting Information tab will open.
In rare cases, extensions are installed globally, into the Firefox installation folder. See this Mozilla Developer Network article for more information. Follow these steps to remove a globally installed extension:
Based on information from Uninstalling add-ons (mozillaZine KB)