Re: > Any ideas as to where it could come from?
"Google only needs Firefox as long as it's market share is significant. If Chrome becomes dominant and Firefox drops to something small (say sub-10%) then why pay them $$$. Based on the uptake of Chrome that may well not be too far off (although most Chrome growth so far has come at the expense of IE, Firefox has dropped a little)"
Broadly accurate, but Google do also make money from the advertising that Firefox sends their way. Google is the default search bar in Firefox as well as (last time I did a fresh install) being integrated into the default home page. If Chrome takes over (and I still rate Firefox as the better browser, but it is now the slowest of the big players (behind IE, Opera and Chrome), then it will still be worth some of Google's while for the ad revenues. But maybe not quite as much as before.
Firefox was backed by Google because they wanted to unseat IE and quite frankly, Firefox was much more capable than Chrome at doing that and was already in the fight at the time. The question is with so much money pouring in, could Mozilla foundation adapt to living like they used to, without the huge amount of resource and management that Google have paid for?
Firefox gained a lot of traction because it was (a) the Open Source champion and (b) had better developer tools than IE. IE9/10 has reached parity with Firefox for developer support (don't downvote me until you've actually tried them properly, thanks) and Chrome might try and usurp it's role as (a). Even though I think Mozilla has greater claim than Google in that regard.
Personally, I would choose Firefox over Chrome ten times over even though it is a bit slower, simply because I dislike the way Chrome's objective is getting advertising data on you. (Yes, there is Chromium, but that will always be second fiddle to Chrome so long as Google are at the steering wheel of development, for the same reason Mono on Linux will always be second fiddle to .NET on Windows).