Passable Rated 3 out of 5 stars
It might be personal but I find Firebug confusing and not at all intuitive. I find IE developer toolbar (awaits flaming) much easier to use. This is a great add-on for Firefox, but not my first port of call when inspecting pages. When ever I need to really dig down into whats going on on a web page I switch to IE (Firefox is my default browser). Not tried Chrome's equivalent so can't comment.
Overall I would say try the equivalent ones in other browsers, it might just be down to personal choice, and you might like them better.