Unfortunately, the new web developers tools* built into Firefox represent a small subset of what Firebug and Webkit Inspector can do. Since Firebug is not compatible with Nightlies (Firefox 8) and Aurora (Firefox 7), it's a major regression.
The Firebug team has tests running against Nightly. Bugs are caught and fixed fairly quickly. Because we work to catch bugs during the Nightly phase, there should not be much time during which an Aurora build is not compatible with a pre-release (at least!) Firebug, and that would be soon after Aurora is branched.
Given that Nightly is the least stable kind of build and could have other problems along the way, we've reached a pretty good point with Firebug's compatibility.
Of course, you also have the Web Console if you're having trouble with Firebug (and I'll grant that this alone is not a replacement for Firebug!)
ObDisclaimer: I'm the product manager for devtools at Mozilla.
Today I needed to determine if any resources were 404ing on a page. Yesterday I wanted to see the exact POST request my browser was sending. I did both on FF using the inbuilt developer tools. I'm sure they may not replace every piece of Firebug functionality, but I didn't say they did.
> People like you are the major regression to the interwebs. Very seriously.
Sort of like Chrome. Firefox has becoming nothing more than the browser that copies Chrome from this point on. Its market share is already starting to slip away and it won't be long now before Firefox is the next Netscape Navigator.
App Tabs,
In-content UI (like preferences in a tab),
HTML/CSS/JS extension model and about:labs (proof on Aza Raskin's blog)
These are just a few things Google has copied from Mozilla. I don't go around complaining about all the thing Google has copied from Mozilla, but the record has to be set straight, Mozilla is not following Google, they are going there own way. They implemented sandboxed Flash first and compartments which Chrome is missing.
Funny that Google haven't updated the Google toolbar.
"It doesn't take a conscious effort to make software incompatible. All you have to do is not work too hard at fixing bugs—which, if you're a big company, you produce in copious quantities. The situation is analogous to the writing of "literary theorists." Most don't try to be obscure; they just don't make an effort to be clear. It wouldn't pay." - Paul Graham
http://paulgraham.com/microsoft.html
I do a lot of Firefox extension development. Many companies or users have a need for highly specialized functionality built into a browser, and Firefox provides an very rich platform for that. You can easily build powerful applications that integrate tightly with Firefox.
Chrome's extension capability is much lighter and more restricted; Chrome extensions are just light little packets of functionality that add to the browser. There's many things that you can't do that you could do in Firefox.
I think that area is definitely where Firefox wins, and will probably continue winning in the future.
Does everyone need that, and is it enough to keep a large market share? I don't know...but it is something that Firefox does better.
Unfortunately Mozilla is intent on squandering every last advantage they still had by copying what Chrome does.
They abandoned XULRunner and Gecko as independent platforms. They're committing to breaking every traditional extension every 6 weeks with the new release cycle (and told institutional users to go fuck themselves). The new stable extension APIs will be limited just like Chrome.
Companies will just switch to modern IE, Iceweasel, or Safari to get a maintained shelf-stable browser. Everyone else will use Chrome.
It's definitely a difficult transition time for Mozilla/Firefox, and I think they're struggling to find their footing. I'm not sure if all the decisions they are making are correct, but as time goes on I think their plans are coming together more.
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Plugin incompatibility is a problem at the moment, but they have systems in place to help mitigate it. If they can manage to keep it temporary, I think they can survive.
I don't have much experience with the new extension SDK, so I can't comment on it authoritatively. The old system is not without problems, and I'm actually glad that they are moving over to something closer to Chrome in terms of certain things...
