Derek752 said

If Firefox is closed it will not open again. However it does show up as being open in task manager. Ending task in task manager will not clear it. This is a new problem after several years of use. The only way to get it back is to restart computer.

Hi Derek

Sorry to hear about this. First of all try the reset feature

Refresh Firefox - reset add-ons and settings

Allow Firefox to start from the default homepage, rather than the previous session, or a list of tabs.

Have a try and then post back with how you get on.

Done all that. - Nett result is that I have now lost all my history and bookmarks. Still only opening if its the first thing I do after turning machine on - Shows as running in Task Manager after attempting to open - (@16.3 Mbyte plus a separate 1.8Mbyte for each additional attempt)

Do you have the Firefox icon on your quick launch? Right click on it, and select Open New Window. Sometimes this works. If it opens, close it by Menu > File > Exit.

This is not a cure but will make it easier if Firefox locks up in Windows. https://support.mozilla.org/questions/997866 {web link}

Tried that - not a solution