[ctnb]

You have to use Firefox Developer Edition and change 'xpinstall.signatures.required' to True in about:config

[mehrdadn]

What about the part where I wrote

> Yes, I want Firefox stable. I don't want to run a buggy browser.

? Is the developer edition running the same code as stable?

[hcs]

Developer Edition is essentially Beta with a few changes (which means additional telemetry by default so probably not up your alley):

https://hacks.mozilla.org/2017/04/simplifying-firefox-releas... (edit for better link)

[mehrdadn]

Yeah, I neither want beta nor telemetry...

[hcs]

fwiw even Nightly is quite stable these days, I can't remember when it last kept me from getting work done. And the addt'l telemetry is just a pref away.