Xmarks was one of the best browser synchronisation services around, syncing bookmarks, passwords, open tabs, browser histories and more across all your Firefox, IE, Chrome and Mac OS X installations.

Unfortunately, being great isn’t much use if you can’t turn those features into cash. And in a new blog post, the company confirmed that “We weren’t able to find a sustainable business model for Xmarks [and] time and money have run out, so we’ve made the difficult decision to shut our doors.”

If you’re an Xmarks user then there’s no immediate need to panic. The company say their service won’t be shut down until January 10th, 2011. And even then, their server disks will be wiped, so your data won’t be sold on to any other party. Although, if you prefer, you also have the option to delete your account at any point before the deadline.

Exactly what you can use instead, though, isn’t exactly clear. Xmarks have suggested alternatives for each of the browsers they support, like MobileMe or Windows Live Essentials, but these are far more limited in scope.

If you’ve become used to having all your browser data in sync, then, we’d say the best alternative is Firefox Sync.

The add-on only works with Firefox, but otherwise it’s the closest in functionality to Xmarks, syncing bookmarks, passwords, history, tabs, form fill data and more. And because it’s also now a standard feature in the Firefox 4 beta, you can be sure that Sync won’t be going away any time soon.  We think it’s a service you can rely on, and one that should only get better in the months and years to come.