I would not consider Firefox to be a "top-notch" Mac app. Every time I used it it felt slow, awkward, and clunky. I'd even find myself using non-native keyboard shortcuts (despite the native ones being available; e.g. F5 vs. Cmd+R) simply because it took me out of the "Mac native" world. No matter how close its emulation came there was always something to throw me off, mostly little GUI idiosyncrasies.