Absolutely. You would never be able to do something like http://conkeror.org in Chrome. At one point I tried to change some key bindings in Chrome, and I had to spend 2 hours recompiling the whole thing; it was an absolute nightmare.
Not quite. Mozilla is a platform with which you can build apps. Firefox is by far the most popular app running on the Mozilla platform, but there are many others, including SongBird, Thunderbird, etc. The bare executable for the Mozilla platform is Xulrunner, and that's what Conkeror uses.
Anyway, the one thing that keeps Firefox competitive is that they built a platform in a fast yet very awkward language, then they built an application on top of that using a much more pleasant, flexible language. None of the other browser vendors understand this; Chrome devs parrot the "but Javascript is too slow to build our UI in" even though they have the fastest JS engine in the world. It boggles the mind and cripples them in the long term for anything other than your standard point-n-grunt interfaces.
