I apologize if this was already answered, but
why do add-ons need a certificate? How to I disable this?
I am using Firefox v54 because I don’t want to lose the
add-ons I have. Many of which have not been replaced
with compatible versions for the Quantum Firefox.
There used to be a temporary about:config preference in the 42‑48 era, but that has since been removed from mainline releases (it still exists in Nightly and Developer Edition).
You can still however use about:debugging to temporarily load unsigned extensions, but you’ll need to do this every time you start Firefox, since it’s intended for extension development.
Can you provide instructions for this?
Thank’s for sharing. But I still wonder why
add-ons need a certificate. It makes no sence to me.
It’s (very) necessary to auth the publisher, for example some 3rd-party source may offer a -popular- Firefox extension and their version could be malicious. There can be many reasons. 
*extensions are granted all sorts of permissions to the browser once installed; & anyway, this issue’s been resolved.
Thank you for your time.