From the US Patent and Trademark Office, Foxmarks applied for a trademark on Dec 16, 2008 for use as
Providing a website that gives users the ability to synchronize, back up, and access Internet bookmarks and passwords; providing a website that displays information, statistics, user reviews, popularity rankings, and related sites for websites and topics of interest
It could be argued that we have prior use rights since we used Xmaks before that date.

Brian