Firefox hangs immediately at startup ever since the latest "update" and it is totally useless

Since the latest Firefox update, it hangs immediately at startup. Now it never works, while other browsers always work. This is a fully updated Windows 10 computer. Even when it does work, Firefox's special tabs - About, Close Firefox, Restore session - are often big trouble; and it seems possible one of these may be the problem now. When Firefox is working. it either closes slowly or not at all, bringing always problematic "Firefox is already running - Close Firefox" messages. When one Firefox window is closed, Firefox always keeps the window that is causing trouble in the first place. So, two things. 1) Firefox doesn't work at all. If you fix this problem with an update, the update must start immediately because clicking on "Download Update" too will be hung. 2) You have terribly problematic special tabs which I have named above. It is my opinion that you cannot fix them - you have to rebuild them from scratch - otherwise they would be working properly right now. I have fallen back on Microsoft Edge which always works. Firefox is never working. Think about it.