Four addons to combine Firefox UI elements and save space
Nix that needless file-edit-view menu with this addon. Personal Menu can take the whole mess and cram it into three (or fewer, if you like) tiny icons on Firefox's navigation toolbar. I wrote about it recently, and it's become one of my must-install addons.
Combines the two buttons so that stop is displayed while a page loads and reload once it's fully displayed. This addon is old - it hasn't been updated since November 2006. Nevertheless, it works as well as or better than other FF addons designed to do the same thing, it's not experimental, and it works just fine in new versions.
Back to Close
Suppose you've backed up as far as you can go in a particular tab's history. A grayed-out back button really isn't that useful anyway, so why not replace it with a close button? That's precisely what this addon does, and it also works with mouse gestures and the alt + left arrow hotkey.
Firefox addon irony, thy name is Fission. Contrary to what the dictionary tells you about fission splitting things into smaller bits, this addon takes your Firefox status bar and merges it with the address bar. Fission also provides you with a few customization options like selectable color or background image. One downside: it may ugly up your theme a little bit by spilling outside the borders of the address bar.