[baku-fr]

I did exactly that, it worked on Debian however not on Windows:

1. Type about:config in URL bar

2. Change xpinstall.signatures.required from true to false

3. Restart Firefox

[javagram]

Debian modifies Firefox builds to set a build flag to allow this preference to work, I believe? The default Windows and Mac builds of Firefox ignore this preference.

[ishitatsuyuki]

It's the opposite: builds compiled from the source allows changing the flag, those builds from Mozilla have the option disabled.