Most, yes. Some people prefer Coke, some people prefer Pepsi. Some people like Firebug and the other various 'Bugs, and the full versions are only made for Firefox. Additionally, any dev worth his salt is testing his projects in all browsers, not just Chrome. Lastly, some people straight up don't like Chrome for various reasons, so this is just another option for them.
So if you do use Firefox, this would appear to be a more feature rich version than the regular version, so it would make sense to use it over the other one.