I use Firefox on all of my devices. Phone to tablet to PCs. Sync works flawlessly, bookmark management and awesomebar are still superior to chrome. Chrome feels lighter and faster in the beginning, but eventually will leak memory and in the end, both Firefox and Chrome, are very resource hungry. I tend not to reboot my machines for a very long time (several months), so these performance issues might not hit all users.
Anyway, I believe Mozilla is struggling a lot and will eventually die, if projects (or innovations as a result of them) like tackling parallel JavaScript or Servo won't add benefits in any way to their programs and products.