[A1kmm]

I worked around this with a script that patches the omni.ja zipfile to change the setting to require signing.

It needs to be unpatched for updates - I don't allow my normal day-to-day Firefox instance to write to it's own binary anyway. Firefox tells me when there is an update, and I then restart into my special script that unpatches, runs Firefox with permissions to modify itself and a profile that I don't use for day to day browsing, only for updates, and then patches it again.

Scripts to patch / unpatch it are here: https://github.com/A1kmm/enable-unsigned-firefox-addons