Google stopped innovating the "Browser" for legacy versions of their operating system. Just like Microsoft. However, the Marketshare of legacy Android is still huge, all stuck with the old "Browser".
Chrome only supports ICS, which accounts for only about 7% of Android devices. Firefox for Mobile supports Froyo (Android 2.2) and above, which accounts for about 87% of Android devices.
The disappointment is that you can't do the same for WebViews inside an app- I like to make apps using HTML5, and it would be very easy to make cross-platform ones if the Android built-in browser was any good. Sadly, it's not, and I don't have any means to embed a Firefox WebView.
I think the problem is that in all versions of Android the stock browser is distributed with the OS. It's not an installed application that can be upgraded independently. As I recall Google went through some pain to separate the GMail app from the OS so that it could be updated on its own schedule, and the pace of innovation in that app has increased.
I would have liked to see them do the same for the browser app a long time ago, but in a way having Chrome as a separate app achieves the same goal going forward if it becomes the default.
