Nifty add-on, and at the same time you could just left click the Firefox window and de-select [menu bar] to hide the menu.
Not to poo poo on the add-on. Just wanted to point out another thing that makes Linux great as there are so many ways to go about customizing these things.
After 6 years of using Linux Lite the mindset changes where you just take it for granted.
Never looking back to windows -Thanks Linux
-yea I can see if you only want the FF to be like this.