Why is the rise of Chrome considered a threat to Firefox? To my way of thinking, having several competing browsers is definitely a very, very good thing. God help us if we end up back in the same boat when Internet Exploder was the only choice.
Face it, there is always going to be tension between those that want a bare bones browser and those that want something more feature-rich. Google is already running into this. There are all sorts of people saying "Gee, wouldn't it be great if Chrome did <INSERT FAVORITE FEATURE>. Besides, if someone did fork Firefox, what would they take out?