So I tried dragonfly in alpha stages (I thought it was the actual full release) and was let down. I read a post on sitepoint about it being out of beta yesterday and tried it out again. Firefox sucks on linux so I am very happy that dragonfly is so good now. It beats firebug in every way imo. You should try it out if you haven't already.
I've been using Dragonfly since they first introduced it, and the new update is much easier to use.
They did a full UI overhaul, and have improved the speed drastically on a few things, as well as having added a few new features (The new screenshot utility is useful to grabbing colors off a webpage).
I have to admit, After reading this thread I did take a peak at dragonfly and quite liked what I saw. That said, I'm used to firebug now and feel it does what I want and the memory leaks have since stopped for me after upgrading.
Edit: Bollox have the memory leaks stopped it's hitting 600kb again. I just haven't noticed because I have a new system with 8 gig of ram.
My old system was 1 gig ram total. I just couldn't bare it anymore and made the upgrade because whether i like it or not firefox is need for the work I do. Trust me I know how your feel Kim. I bet you just want to rip firefox's heart out. I know I did at times.