Firefox still feels non-native on OS X as a result of its reliance on XUL. My main issues are around UI. The menu bar only fully populates once the browser is almost loaded, not when the browser is first opened. The other thing is that UI elements exist in an uncanny valley, where they are not quite native, but not quite foreign.

Camino meant to fix that, but it has moved onto greener pastures.

See jorvi's comment: https://news.ycombinator.com/item?id=19264960 there are some bugs that drive me back to chrome when I try it