I tried some FirefoxOS phones for about 20 minutes @ fosdem. As a developer the idea of native html is tempting. As a normal user I'm rather unimpressed. "What can this do, that my Android can't?" Without the answer to that question, people won't get it.
For this (as I share his opinion), read the article from my collegue Sergi Mansilla about the promise of Firefox OS: http://sergimansilla.com/blog/promise-of-ffos/
Paragraph 1: Ok, so we have some serious competition.
2: We are not going to beat them, we are changing the game.
3: There is massive developer potential.
4: Html sucks, or does it?
5: Frameworks and compile-to-js save the day!
6: Not just HTML5, standardized HTML5!
7: Fixing the problem of "Several languages, frameworks, APIs" and "vendor lock-ins"
8: Mozilla can be trusted.
So 2, 6 and 7 are the big promises. And 3 and 5 is how they are going to do it. My question is this: yes there are lots of web developers, but are they skilled enough for more advanced challenges? And are you really solving the "Several languages, frameworks, APIs" problem? One could argue that there are way to many javascript compilers, frameworks... already!