Firefox install unsigned add-ons

Since Firefox 43, it won’t allow you to install unsigned extensions.

While it’s a good thing, you can revert it in case with the following steps:

To disable signature checks, you will need to set the xpinstall.signatures.required preference to “false”.

• type about:config into the URL bar in Firefox
• in the Search box type xpinstall.signatures.required
• double-click the preference, or right-click and selected “Toggle”, to set it to false.

It will eventually show your unsigned extension with a warning but it should work out fine.

References:

• https://wiki.mozilla.org/Add-ons/Extension_Signing