Firebug can be really slow, but I just can't change it to Chrome dev tools, which seem unintuitive for me in many places (and which stop me on non-existing breakpoints randomly, no, I don't have "break on exceptions" enabled or anything like this).
Regarding Fx dev tools, they e.g. do not show evaled scripts at all in the JS panel. Also I don't see a way (yet) to have debugger and console visible at the same time. And there are many other tiny Firebug goodies not implemented yet here and there. Firebug will be still essential for me for many months.
Actually they address that as well, albeit from a philosophical standpoint -- Firebug is supposed to provide useful web development features that aren't already served by the browser. There isn't supposed to be competition.
I suppose, in the near future, some redundant features will be cut from Firebug.
Well, I find the FireQuery extension for Firebug (http://firequery.binaryage.com/) very useful. Though it could probably be ported to the native developer tools, it probably won’t be, at least for a while. So Firebug is useful for backwards-compatibility with custom extensions.
