Firefox 41 requires that extensions be signed by Mozilla, which follows a brief review process. Perhaps the publisher of that add-on will take care of that before Firefox 41 is officially released in about 5 weeks. Would you want to run the current release, Firefox 40.0.2, instead of the beta test release? It doesn't block unsigned extensions. You can grab that here (scroll down to your preferred language): https://www.mozilla.org/firefox/all/ Alternately, you can flip a setting that exists only in Firefox 41 to allow unsigned extensions. That can be found here: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful. (2) In the search box above the list, type or paste '''xpi''' and pause while the list is filtered (3) Double-click the '''xpinstall.signatures.required''' preference to switch it from true to false Does one of those suggestions resolve the issue?