Opera has a ton of features that firebird doesn't have (or any other browser for that matter)

Has firebird implemented mouse-gestures yet? Drag-and-drop toolbars?

And generally I find the new theshadow releases tend to follow on the heels of burst, and the other clients follow on the heels of theshadow... I guess it's whether you prefer to get the innovation from a dealer or straight from the grower ;)