I do not think there is such difference in FF and CR performance. Both browsers are relatively close. Firefox however hangs in some common cases where as Chrome handles general cases better.
CR however is worse when it comes to multi-tab browsing with over 20 tabs!
Yes, with just a few tabs open Chrome's multi-process architecture shines at cost of being a memory hog. As a result Chrome starts thrashing long before FF.
FF 8-13 really shined in memory usage. Unfortunately even by their own internal benchmarks, it's gone downhill since since 13.
CR however is worse when it comes to multi-tab browsing with over 20 tabs!