Hi, Since version 43, Firefox requires add-ons to be signed. Back in February 2015 [https://blog.mozilla.org/addons/2015/02/10/extension-signing-safer-experience/ it was announced] that, for a safer add-on experience, all extensions will have to be verified and signed by Mozilla before they can be installed. More insight into that decision is contained in Mozilla's [https://blog.mozilla.org/addons/2015/04/15/the-case-for-extension-signing/ April 2015 blog post]. Extensions hosted on addons.mozilla.org are automatically signed. If an extension you wish to use is distributed by a third-party, it must be signed before you can install it. Unsigned extensions that you have already installed will be automatically disabled. Please ask the add-on developer or vendor if an updated and signed version of the add-on is available. You can also visit addons.mozilla.org to see if there's a signed version of the add-on you can install, or an alternative add-on which would provide the functionality you want. Best regards, Michal