I switched and while I use it daily, even on plain installs it has huge, huge memory footprints. I thought switching over was going to be a huge memory saver over Chrome, but it hasn't proven to be the case for me unfortunately.

And of course, it "doesn't" support USB keys like Yubikey, as in, it totally does if you change a config flag, but websites like Vanguard and even Google just check user-agent and if it returns Firefox, it prompts you to use other methods because the key "isn't supported."