No problems until last few weeks. Now when I try to start Firefox after booting PC (Windows 10) it mostly works, not always. However if I accidentally exit from Firefox it will not start again unless and until I reboot the PC. A particular problem manifests when invited to upgrade to 54.0.1. I go through all the motions, it downloads the update, then it says it is going to restart Firefox. It does not restart, will not start manually. When I reboot and mange to restart it is still on version 5.0. Tried this several times, on PC and Laptop. At some point in investigating why it would not restart I saw message saying Firefox cannot start because already running. Sorry I cannot remember where I saw that message. I then looked at list of all running processes on the PC, and saw that a thread of Firefox was indeed running but I have no means of waking it up to use it. I tried to kill it but kept popping up. Only way round is to reboot the PC. Is this a probem now I see that the latest versions run multi-thread? Rebooting is a very cumbersome get-round, but I am still unable to load and use version 5.1.0. Exacltly the same symptoms happen on my Windows 10 Laptop, so I really do not think it can be just my problem. Please can someone help.