Use "Firefox/File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit") to close Firefox if you are currently doing that by clicking the close X on the title bar.

thanks, that works, but it requires a bit of effort to change habit. it can be a bit inconvenient to do instead of a quick alt+f4

Alt+F4 only closes the current window and not the Firefox program with all open windows.

• Close Button: https://addons.mozilla.org/firefox/addon/close-button/

yes that is exactly the problem , here's the sequence :

normally i only open 1 firefox window, and it has all my tab groups. so i am able to open/close firefox and retain these tab groups.

and then there are times when i just have to open a new window, and unfortunately, there are times when

- i close my base window first ( the one with the tab groups )
- then i am left with the new window ( which no longer retains my tab groups )
- i have no choice but to close this new window

when i reopen firefox, i no longer have my old tab groups. so this is where my problem lies. of course if can make the habit of always going to firefox > exit, at least the tab groups are always available.

it would have been great if these tab groups are stored permanently, like bookmarks. it just feels convenient to use.

So, just to be sure, if a case like this does happen (such as mistakenly 'x-ing' out a window), there is no way to recover the massive amount of tab groupings?

If you close a window by accident then try to restore that window via the History menu (Recently Closed Windows).
That may also work on a next start, providing session restore is working properly.