GC.Communicator.exe

I ran this as required by 'Open With Google Chrome' and it completely messed up Firefox, all my addons were gone, all my customisations were gone, years of personalization gone.

I don't remember this needing an extra program to work. In my case I had to run system restore to get Firefox back the way it should be.

I couldn't find what GC.Communicator.exe installed either with standard uninstall or IOBit Uninstaller. Since all my addons were missing, I couldn't use the addon itself to uninstall it either.

This is a dangerous mess.