Rated 5 out of 5 stars
Wonderful!! Just what I was looking for :) It seems to restart MUCH faster than hitting the 'X' and reopening.
I'm guessing it will also reduce the likelihood of me getting the "Firefox is already running, but is not responding. To open a new window, you must..." message.
I like this in the File Menu, but the toolbar button needs to look a little less friendly than what it looks like now. Maybe a Spinning Firefox (think Sonic the Hedgehog)...something that wouldn't accidentally be mistakenly hit by a guest on my computer thinking it's the reload button, which is almost exactly what it looks like. Maybe a dropdown menu asking for a close second click would work. I'm just concerned that I might accidentally restart while in the middle of something important. I like my computer to be idiot/me-proof ;)
There's also a keyboard shortcut I just found. I won't be disrespectful to the add-on developer and tell you what it is here though. But I do want you all to know it's an option.
Thanks for another great addition to the greatest browser in the world =D