XMarks is the only thing that will sync Safari with Firefox
And, it's leaving us:
"The past four years have been a wild ride for us: growing something from nothing to substantial scale, providing a simple service that people love because it simplifies their lives. We’ve learned tons along the way, often by making big mistakes. We’re really sorry that this last lesson means that you’ll have to find an alternative to Xmarks, but the alternatives exist and you’ll have no problem finding them." (from Xmarks Blog)
Again this shows how good ideas don't always win.
This was an excellent idea, but perhaps it suffered from the classic-cliche- VC-quip "It's a feature not a product", or worse, "It's a product not a company". I don't know how much money, not to mention blood, sweat and tears, was spent on trying to get it to achieve escape velocity but I can imagine that it was considerable.
Having built and attracted huge numbers of loyal users is a major accomplishment, even if it didn't lead to a sustainable business. Kudos and all the best to the team.