Current Firefox releases require extensions to be signed to prevent abuse by malware. In Firefox 43 unsigned extensions will be disabled by default. You can set xpinstall.signatures.required to false to disable this security feature in Firefox 43. In release and beta builds of Firefox 44 and later you can no longer override this. See: *http://www.ghacks.net/2015/12/16/what-you-do-when-firefox-disables-installed-add-ons/ *https://support.mozilla.org/kb/add-on-signing-in-firefox *https://blog.mozilla.org/addons/2015/02/10/extension-signing-safer-experience/