-has more glitches (things doing plain weird or not working sometimes)
-requires "activation" of each panel and reloading of the page
-sometimes suddenly opens for no reason when you visit a webpage without the intention to debug it
-is impossible to use if you want to debug a project with hundreds of js files (e.g. uncompiled JS of a large project) because it has a bad type of dropdown for selecting the JS file
-generally just requires more clicks and more frustration to get things done
The one in Chrome:
-has a better console (easier to type commands, inspect variables, etc...)
-works immediately as soon as you open it (no "this panel was inactive during page load")
-has more features
Note that I was talking about Firebug here. Firefox also has its own dev tools, at least an "Inspect Element", with even a 3D view of a page allowing to see divs outside of it and so on, and that one is awesome!
I'm curious from your side (maybe also to learn a thing or two about Firebug): How would you compare it to Chrome? What features make Firebug stand out?
EDIT: Why do I need to add multiple newlines between the "-" to make Hacker News post them as newlines?