There's a video somewhere of Mark Zuckerberg and some co-workers discussing ideas about Facebook (in it's earliest days), and in the video they are trying to decide on what options should be available under the relationship field, one guy says something like: "I feel like we should make it possible to say that.. like you're not in a relationship per se, but nor are you free, like it's complicated..."
Back then the number of people involved in browser and web technology was small. Now, even the brightest mind will have any new idea critiqued and iterated by thousands of equally bright minds whether they like it or not.
It's probably too much to say that there are no new ideas in web browsers any more, but it's certainly harder to find them thanks to how collaborative the Internet has made the world (that's almost ironic)