If you aren’t someone to pass up on a little extra space in your browser window, OneLiner is a Firefox extension that will interest you. Provided you don’t have a whole lot of extension buttons riding your navigation bar, this extension can give you a bit of extra space by shrinking the location bar and moving tabs next to it.
Even if you were to hide the menu bar, you’re still left with tabs taking up space and the navigation bar appearing under it. Once installed, this no restart extension shrinks the URL bar’s length and capitalizes on the freed up space by moving the tabs to it.
The extension, developed by Mozilla itself, is extremely similar to the hide navigation bar feature in Chrome to the point that no room has been left for extension buttons. When you click inside the URL bar, it expands to full size, hiding the open tabs and returns to its shrunk state once you hit enter.