I've always wished that Firefox had a "Restart" menu item, and because of that I've used the Quick Restart Firefox add-on quite a bit in the past. At some point last year while the Jetpack prototype was still being developed I even wrote a jetpack to add the menu item in less than 50 lines for a contest that Mozilla had. I used that for a while, but these days I live on the FIrefox nightly (aka Minefield) and both of those old options aren't available to me any longer. So I decided to write a restartless add-on to add a "File" -> "Restart" menu item to Firefox.
I'm calling this add-on "Restartless Restart" and it works on FIrefox 4+, it's 1KB at the moment, and it does not require a restart to be enabled, disabled, installed, or uninstalled. You can find it on addons.mozilla.org here. If you want to contribute, then you can find the project on GitHub, where all of my projects can be found.
The part that I love most is that it's still less than 50 lines =]