Extensions are signed by the Mozilla Add-ons team when they are submitted by their publishers. There's no way for you to do it yourself. (If there was, it wouldn't protect anyone from having malware authors verify their junk.) If you need to use an unsigned extension, try turning off the signature requirement: (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) If the '''xpinstall.signatures.required''' preference is set to true, double-click it to switch it to false Note: This is based on the released version (Firefox 41) but I think that preference still exists in beta (Firefox 42)

See also: *https://support.mozilla.org/kb/add-on-signing-in-firefox *https://wiki.mozilla.org/Addons/Extension_Signing *https://blog.mozilla.org/addons/2015/02/10/extension-signing-safer-experience/