Gecko pushed forward too. Then they stopped, they got large and bulky. Things changes, one day Webkit won't be the ones to be first with the new. Competition fuels this process.
We should have learned this lesson from Internet Explorers dominance in the past.
WebKit isn't the first with the new today. In terms of features Firefox and Chrome (not WebKit generally, specifically Chrome) are pretty much neck and neck. They each have their priorities which reflects which "beats" the other in specific features. Chrome has already released Web RTC and Web Intents, Firefox has already released calc() and (current) IndexedDB.
I think you're referring to Firefox from a couple of years ago, their pace has ramped up since they moved to rolling releases.
Well, I am referring to the image the (slightly techish) public has of Firefox as an outdated, slow competitor to Chrome. As I follow it's development closely, however, I am aware they are getting better again and this I why still use it as my primary browser.
We should have learned this lesson from Internet Explorers dominance in the past.