Seems like one more nail in the coffin for Chrome versus alternatives which have a higher degree of people's true best interests at heart.
As a side note, this really deserves a blog post or singular site/page that explains the issue in a simple enough way so the word can spread.
There is some thought that if Apple opens up iOS a bit Chrome could make more headway there as well.
Numbers I've heard are Chrome - 60%, Firefox < 5%.
One of the main things i've noticed is a very jagged divide in performance. Firefox's renderer is generally faster and has fewer bugs, but with some APIs like canvas it's a mixed bag, some things are very slow due to significant implementation differences such as fillText. Even for the JS engine it's not so clear cut, everyone thinks of V8 as the king, but there are some cases that chromes optimizer is extremely sensitive to such as global variables.
Firebug was amazing, and predates Chrome by two years.