I don't see how to add Add-ons to that list. Here are a couple more:
* Restartless Restart https://addons.mozilla.org/en-US/firefox/addon/restartless-restart/ MIT/X11 license
* Hide Tab Bar With One Tab https://addons.mozilla.org/en-US/firefox/addon/hide-tab-bar-with-one-tab/ MPL 1.1 license
