firefox has more features and allows more customization and i more battle hardened in terms of security.
google chrome is faster (allows for load balancing across multiple CPU cores)
A way to see a night and day difference between the performance of firefox and google chrome is to try to quickly load 50 or so tabs, they will load significantly faster and you will see that every CPU core will max out.
Even though the overall functioning of the browser is single threaded, each tab has it's own process and it attempts to equally distribute the tabs across multiple cores.
(a evolutionary step from this to have resource based distribution so if some tabs are very CPU intensive, they can have fewer competing tabs on their cores, and ultimately bringing about true multithreading for the entire browser as a whole)
Firefox is my favorite browser as it offers the functionality that I want (and chrome fails to provide)