Firefox own developer tools won't log ajax calls in console. Firebug does. This and the fact that you need to open the settings tab to enable preserve log are my problems with Firefox tools keeping me on firebug.
Personally I've switched back to dev tools in the developer edition, mostly because the ability to see which elements have events attached from the markup view is very useful.
yes convenience, saves time switching back and forth. chrome didn't have this feature either but they recently added it (even though not as good as firebug's since when you click on the entry in the console it takes you to the network panel and hightlights the entry rather than opening it up automatically)
Hit the little arrow next to it. You can select Errors, Warnings, and Log. Log makes xhr network requests show up in the console (just like the network tab). I don't know what you mean by "fills up the console".
One advantage is that there are plugins, like YSlow from Yahoo, that are available for Firebug. Though the article notes that plugins don't currently work with the Firebug 3 alpha.
YSlow is pretty useful, both as a developer and when attempting to demonstrate potential problems with a site's performance to others in an objective way.
Besides: a plugin with its own plugins is just cool.
I think Firefox Dev Tools may have reached parity with Firebug. Up until recently (~3 months), Firebug was superior in network, more informative in console when using console.log for objects, resizing, etc. Still, Firebug does have add-ons
Firefox Dev Tools still has some gigantic bugs that make it unusable for a lot of scenarios. For example, it doesn't show evaled code in the debugger. Which means anything that dynamically creates code (common in development) can't be debugged. Shumway (the Firefox flash compiler) for example.
Believe me I've been following this issue closely for a long time and know the status. While the large work that was needed has been done, it hasn't been fixed completely. In my case I get evaled items to show up but they 1) don't have actual names just foo.js -> eval and 2) don't have the actual source shown. I think this might be the issue that is blocking me: https://bugzilla.mozilla.org/show_bug.cgi?id=833744
So while this is "on the road" to being fixed, it's not fixed completely.
Using both is sort of needed at the moment. Firebug for example doesn't do source maps. Also, firebug is too slow for some pages I've worked on. But of course firebug does some things better still.
