And the just-concluded Firefox Extensions contest may just be the first step towards doing that. See http://developer.mozilla.org/contests/extendfirefox/
The Reveal and Showcase are indeed jaw-dropping extensions!!! Try em out and you'll never go back to IE.
And to think this are just first-gen extensions. What more stuff can come out of the community once a full-pledged XUL IDE comes out!
One thing that Firefox team should also do is to create a Firefox SDK, that not only includes a XUL IDE, but an easy way to create Firefox Skins. The skinning system is already in place, but a WYSYWIG way to do it would further bolster adoption.
Its not only eye-candy, but a WYSYWIG skin editor will allow corporate IT environments to come up with their own internal distros. For example, disable Check for Update to check the Mozilla site and instead check their internal version. Some other customizations like predefined internal links, bundled extensions, a secured Extensions Manager, etc. etc.
The Firefox SDK along the lines of Visual Studio user-friendliness will also make it easier to convert corporate IT folks who are used to the visual environment.