Perhaps it has to do with the contributors being expert UI developers, and firebug developers second. Whereas the other tools are mostly developed by employees who do full time dev tool development, but not so much work using the tools.
But I know others mostly prefer chrome tools. The same people often get stuck in firebug or in IE dev tools.
Anyway... GREAT WORK FIREBUG TEAM! xo
As far as I am concerned they are the same in that regard. And since both of those tools are not built by "developers", but by "frontend engineers" it doesn't really matter.
I spent like 15 minutes trying to figure out how to attach Firebug to the browser window. Only to find out that the upward pointing arrow in a gray circle means attach to browser window. On WebKit I click an icon that looks like a browser window with developer tools.
The resources tab in WebKit is ten times better then the mishmash of CSS/Script/Net/Cookies tabs all spread out.
Anyways that is just my opinion, and as far as I am concerned Dragonfly was the best.