Earlier quoted context omitted.
I've pretty happily switched to Chrome, which seems to do everything I used to ask Firebug to do. Although honestly I no longer use Firebug because I no longer use Firefox, and I no longer use Firefox because it takes up an obscene amount of vertical real estate compared to Chrome.
My Firefox takes up less vertical real estate than Chrome. I use Tiny Menu, customize the toolbars to put everything into the menu bar, and use Tree-Style Tabs to show the tabs vertically along the right side. The best option I have at work is Chrome, and having the tabs along the top is much less usable compared to Tree-Style Tabs.
I prefer Chrome these days but Firefox and Safari are still up there, and also fast[1]. It's just nice to have a variety of good browsers to choose from.
[1] http://arewefastyet.com (doesn't say "no" anymore)