So are you saying that when I am finished (say for the day) I should quit Firefox? I should not bother closing windows?

Thanks cor-el. Are you saying that if I'm finished for the day (say) and want to shut down or not use the computer, I should Quit Firefox and should not close my windows?

You can quit Firefox while all Firefox windows and tabs that you want to restore are still open. If you have selected "Show my windows and tabs from last time" as the startup setting then you should see the tabs on the next start. Otherwise you can use "History > Recently Closed Tabs/Windows".

Thanks cor-el. I always had "Show my windows and tabs from last time" as the startup setting. But the computer didn't do that and so I lost all my tabs.

I guess my mistake was that I didn't immediately go to "History>Recently closed tabs/windows".  I probably quit Firefox in my panic,
maybe more than once, and by that time my "History<Recently closed Tabs/Windows" no longer gave me the lost tabs.
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My reply was cut off. Continuation is: closed tabs/windows" did not have my lost tabs.