Extensions that do not have a "Remove" button are installed by other software and are not under control of the Firefox extension manager. Such globally installed extensions are usually found via a registry scan or are installed in a location that Firefox scans for installed extensions. *https://developer.mozilla.org/Installing_extensions *https://developer.mozilla.org/Adding_Extensions_using_the_Windows_Registry Extensions installed this way need to be removed via the settings (options/preferences) of the program that has added this extension or this program has to be uninstalled via "Control Panel > Programs". In Firefox you an only disable such an extension. ---- You can check the extensions.json file in the Firefox profile folder for details about this extension. You can open a JSON file in the Scratchpad (Firefox menu button or Tools > Web Developer). Click the "Pretty Print" button to format the file for readability. *https://developer.mozilla.org/Tools/Scratchpad