We have heard it before that the Addons can interfere with the proper functioning of Firefox. If there is a problem, than one of the first things to consider is to run Firefox without the Addons. What seems to be happening is that with each new version of Firefox, there is the possibility that one of the Addons will become problematic. The Addon called "Firefox Color" would hang up the Firefox Browser when it was first opened. I have the Bar on top set to certain shade of Blue, and the Browser would start with the wrong color and takes several minutes for the right color to appear. Meanwhile the browser would be hung up and non functional. I would wait several minutes and could not browse. Firefox was waiting for something to initiate and became nonfunctional during that period. After several minutes I would shut Firefox and reopen, and get that ANNOYING MESSAGE... Firefox is still open. So I am trying again and again to get the Firefox to enable, and finally the Bar on top changes to the selected shade of Blue and is working again. So what did I do? I disabled "Firefox Color". So I no longer have that problem.