Firefox will not load. Error message " Firefox is already running, but is not responding. The old firefox process must be closed to open a new window"

There are no other instances of firefox running. I have tried all fix suggestions on the net, also uninstalled and reinstalled 6 times. No result. This all started just after firefox added their new tracking blocker features. I saw Facebook and a few others had trackers on my browser which had been blocked. Day later, firefox no longer works. This was couple months ago now.