I'm not too sure if that's possible (I don't know anything about Chrome add-on development), but maybe you can add an event listener to a tab closing and then instantly restore the tab at its previous position without actually loading it.

No, i didn't because when I commented it was't there. However, I'll just remove my vote then.

Imo it's more like a statistic than an indicator for something. This applies specifically to windows. I'm mostly fine with the tabs only displaying the statistics when they are collapsed, but I really do like the idea of having this always in for windows.

Or regexps (exotic).

I would be fine with this, does not make any sense to activate the TO window via TO anyway.

But this one does not restore correctly when closed as the last window. Furthermore it wastes a good 77px in height (with tabs, navigation and bookmarks).

Why not just do it in the popup too, even as an option? Also, I never said that I didn't want the window to scroll at all, I just wanted it to scroll differently like you'd expect in most other applications that use a list or a combo box control.

Looks good here. I don't really need it but if it can be achieved (easily), why not?