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 later Firefox% release and beta builds (47+) you may not be able to override this anymore. See also: *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