So those that are paid to work on the Linux kernel aren't real developers?
I'm sure that even the Linux kernel developers know that their software is not perfect. Every once in a while you see security advisories regarding the Linux kernel and there's even anecdotic evidence about the fact that building software isn't easy regardless
of the platform you're working on (http://www.vidarholen.net/contents/wordcount/). Oh, and the first Linux kernel came out a while after the first NT kernel.
People will ask for more features, but due to its easy extensibility, they don't need to ask Mozilla. The Firefox team will not add everything people ask for. It should stay as a small download (<6MB) - Opera is the smallest download at the moment, but
the next version of Firefox may be smaller than it is now (4.7MB).
Firefox is meant to be a very basic browser, with only essential features used by most people (it does not even have mouse gestures even though people have asked for them -
a third party extension can do that). It has something that Internet Explorer will never have - works cross platform, rendering pages the same, even extensions generally work no matter your OS.
I'm sure there are extensions that are used by companies internally, and they don't have to worry about spending a lot of money to buy a certificate.
Assuming you agree with me that bugs happen, you're essentially saying that pushing bugs away from Mozilla to third party developers will make everyone's life better. I bet that in 5 years from now you'll see things in a different light.