I generally have a "home" Firefox window with my most used tabs pinned. Sometimes I close it before another window, so I was frustrated to "lose" it and having to redo my pins. But recently I discovered this feature. Joy!
Only the last three or so windows though, so if you got a few pop-ups before you press that you might be screwed...
...unless you have backups of an old session file, then you can use this tool to restore a list of those tabs: https://www.jeffersonscher.com/ffu/scrounger.html
There is also this handy addon for saving backups of windows like that to a txt list of urls: https://addons.mozilla.org/en-GB/firefox/addon/urls-list/