Edit: It "magically" work after a restart (?), no idea why I am losing the tab/window history, but this now does exactly what I want, excellent!

Looks great, love the density of information. I tried this add-on to save a window's worth of tabs for later user (project-dependent things). I should have tested it better, though, because on my xubuntu 19.10 with Firefox 71.0 (64-bit) the tabs do not restore at all (it just opens an empty new window), so the extension essentially ate all my saved windows.