Installation aborted because the add-on appears to be corrupt.
I can't install any add-ons, I always get the Subject, I've reinstalled Firefox, Restarted on troubleshot mode reset Firefox and clear starting cache, problems persist!
It is possible that (anti-virus) security software is causing the problem. Try to disable security software temporarily to see if that makes a difference.
Boot the computer in Windows Safe Mode with network support to see if that has effect.