works great Rated 5 out of 5 stars
This is better than minimize-to-tray because with minimize-to-tray we always have to look in 2 places to see whether we have firefox windows: the taskbar and the system tray. Mac OS-X made a combined bar and windows 7 (& vista) partly followed suit.
It would be nice if we had the option to allow us to close any windows normally *except the last remaining window* which would normally cause us to exit.
Another thing I'd love to see is a Restart-on-Close. When you close all your windows and firefox would normally exit, this is a perfect time to Restart firefox and when it comes back up I'd want it to start minimized so in effect it looks like you've simply minimized it but in fact it restarted first. The benefit is that it clears out unneeded memory from firefox and it often runs more smoothly than if you've been keeping it running continuously. It should be the session-preserving restart like the one offered by the add-on manager (or by justin Ƨullivan's "Restart Firefox" addon but not most others), so it preserves tabs and also session cookies, etc.