As a Firefox stalwart, my only sustained complaint about it is that the plug-in architecture is pretty crappy, but that's mostly a minor complaint so long as you avoid installing anything but very well understood and mature plug-ins. Chrome doesn't do all that much better here, since although its plugin architecture doesn't suffer quite so badly reliability-wise, plugins can still violate your privacy pretty much arbitrarily (modulo the relevant appstore blacklisting it, which is a pretty impotent reactive measure, as we've seen).

Firefox memory usage has always been, and I suppose will likely to continue to be far ahead of Chrome, since the desktop implementation is now largely identical to that used in Firefox OS.