The latest Firebug (1.9b1) allows the Firebug pane to be positioned on any 4 sides of the browser (as well as detached)!
I have a widescreen monitor and have much more width than height real estate.
Install the latest beta, hit the Firebug menu and there is a new option: Firebug UI location (detached, top, bottom, right, left). I've moved mine to the left. I also selected Firebug > Options > Verical Panes.