I'm a big user of Firefox's tab groups (typically with 100s of tabs between the groups) and this is definitely not the case. I just tried it out and closing the last tab in the current group will take you back to the group overview screen.

Hmm, I guess I'll have to give it another try.

Edit: I remembered the problem. It's not closing the last tab, it's closing the window that closes all tab groups for that window. More generally, the problem for me is that tab groups are local to a window. In practice this basically means that if you want to use tab groups, you can't also use multiple windows, because managing multiple windows each with multiple tab groups pretty much guarantees that you'll go insane trying to keep track of where everything is and which windows are safe to close.

I think I would much prefer if tab groups were shared across windows, and each window would "claim" a tab group as its own. Closing that window would either close that tab group or even just "detach" from it, leaving the tab group available for another window to claim it. Essentially, it would work sort of like tmux only with windows and tab groups instead of terminals and shells. (Possibly with the limitation that only one window can view a given tab group at once.)

I'd love to use tab groups to organize a large number of tabs, but ultimately, the fact that your tab groups are always a single close button away from being blown away is a deal breaker. (I know I can restore the window to get them back, but that's only if I remember while that closed window is still in the "Recently Closed Windows" menu.)

Another problem with the tab groups in Firefox, is that resizing the window while the tab group expo is open will "rearrange" the tab groups to fit into the window, and won't remember where they were when you resize it back. It's a complete waste of time trying to spatially organize your groups because FireFox knows better.

I'm just starting out on something similar (OCR'ing letters from a word game), so would also love to here more about the process you're using with Tesseract and OpenCV.