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Although at the moment since the release of seamonkey is so new it report not compatible. Simply click on it and 'install anyway' and you should be good to go.
Yup and seamonkey announced they're setting up their own sync server to support their legacy sync feature now since they've teamed up with the thunderbird crew.
Seamonkey is lightning fast... I have firefox installed on my regular system for those few times seamonkey has a hiccup but 99% of the time I'm surfing with seamonkey.