I use all three tools. But Firebug still has features that aren't implemented in both other tools. You can read the Bugzilla entries, sadly Mozilla cut off Fire

I use all three tools. But Firebug still has features that aren't implemented in both other tools. You can read the Bugzilla entries, sadly Mozilla cut off Firebug too early, many minor features (eg DOM tab) were just recently added to Firefox DevTools and aren't working 100% because of glitches and bugs. And Chrome DevTools don't has those features at all. (I use a separate Firefox instance for development, and it's not my number one browser for years because it can't handle hundreds of open tabs - IE and Chrome excel on that (my) requirement for 10 years.)