Is there any chance someone who the add-on does work for uninstall then reinstall it? Just to see if it then gets blocked?
I tried to install it on firefox 50.0 with avast 12.3.2280 on my win7 system as I didn’t use it on that, only on this test system.
It failed to install (disabled) and it is the same AOS version 12.0.88 as in my image2 in Reply #7 above.
Despite having the same about:config settings for xpinstall.values in my first image in Reply #7 above.
Thanks for doing that, DavidR. Certainly something strange is going on.
You’re welcome.
It is certainly weird. The only thing I can think of is I have had the firefox AOS Add-on on this XP system for some considerable time without removing it. Nor have I done a clean install of avast only Program Updates in avast.