It's still slower than other platforms but it's much faster than it used to be. I've been using Firefox exclusively on OS X / macOS for a year. The only problem

It's still slower than other platforms but it's much faster than it used to be. I've been using Firefox exclusively on OS X / macOS for a year. The only problem I've seen is that it sometimes uses more CPU than is reasonable, which often appears to be due to Gmail's terrible implementation.