By default, Firefox requires that all of your Add-ons have been digitally signed by Mozilla before enabling them. If you need to enable an Add-on that has not been signed, use the following steps to disable the requirement.
- Navigate to
about:configin the address bar.
- Search for
- If it exists, set it to
- If it does not exist, right-click to create a new Boolean preference, name it
xpinstall.signatures.requiredand set it to
- Restart Firefox
After restarting the browser, the Add-on should be enabled. It will also display a warning about it not being verified.
(tested on Firefox 47.0.1)