It's so good, actually, that I'd like it to always stay as it is, however the developers have other plans for it. The name was changed from Foxmarks to Xmarks, but it's not merely a linguistic change; the new service is broader and much more ambitious in scope.
Yes, it's still about synchronizing your bookmarks and passwords between two or more instances of Firefox, but now it uses the user generated data to create a site suggestion service, somewhat similar to StumbleUpon. As you browse through the web, you can click the Xmarks icon in the address bar and see information on the site you're currently on, as well as top 5 similar sites.
Furthermore, Xmarks now integrates with Google search; when applicable, it shows an information icon next to the search results; move your mouse over it and see some basic info about the site in question.
Is Xmarks moving into bloatware territory? If it is, it's being careful about, as the new options can be turned off if you don't like them. For me, the most important part of the service is still bookmarks syncing, but I'll give the new options a whirl in the next couple of days and see if they're useful in the long run.
The upgrade to the new version is not mandatory, but it's seamless - I've tested it out and it works as advertised. From the site:
"You can install Xmarks even if you have the Foxmarks add-on installed on your computer. Xmarks will upgrade your current Foxmarks add-on and continue to sync and back up your bookmarks (and optionally passwords)."