I had this same problem, however I uninstalled 360 totally and then reinstalled it from their website. I then installed the FF add-on from the 360 website and it went in flawlessly.. The strange thing is that the revision level went backward (from 1005 to 1004) when I installed the plug in from the 360 website however the update date went forward to July 25 2017 (today) . Hmmm