Even if you were to download unsigned add-ons, Firefox is hard-wired not to allow them to work. What add-ons are you talking about?

Current Firefox releases require extensions to be signed to prevent abuse by malware. In Firefox 43 and later unsigned extensions will be disabled by default. You can set <b>xpinstall.signatures.required</b> to false to disable this security feature in the current Firefox releases. In later Firefox releases 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 *https://wiki.mozilla.org/Addons/Extension_Signing