Hmm, I've never seen that screen before. Is it generated by an add-on?

On Windows 7, you may be able to use the individual window thumbnails on the Windows Taskbar for this purpose, although, once you hit a certain number, it turns into a list...

It's tabsplash. https://addons.mozilla.org/pl/firefox/addon/tabsplash/ And thanks, but it's not enough...and I use Windows on Parallels.

I did a brief search on the Add-ons site and didn't see anything that says it would list your windows, other than

https://addons.mozilla.org/firefox/addon/monitor-master/

which really is directed toward choosing which of your multiple monitors you want to display a window on.

If you don't find what you're looking for elsewhere, you could try this forum: Add-on Ideas / Looking for an add-on • Mozilla Add-ons Forum