Just to point out that by using the hack, some FF extensions report as "corrupt" when you try to install them.
The add-on downloaded from this site could not be installed because it appears to be corrupt.
FF 56.0.2 x64
With the hack installed, so the files; instalDir/mozilla.cfg & instalDir/defaults/pref/autoconfig.js, as it is, the following extensions report as "corrupt" when you try to install them.
> https://addons.mozilla.org/firefox/addo ... -download/
> https://addons.mozilla.org/firefox/addo ... ader_webx/
Now plenty of extensions do install successfully.
Why those two particular extensions don't, can't say?
Is it the particular contents of those two ("hack") files, don't know?
Expected behavior, or a bug, don't know?
STR:
Install the signing "hack".
Try to install above extensions.