Syncmarx leverages your favorite cloud file hosting services to synchronize your bookmarks between browsers. Simply install the syncmarx extension, authenticate with a cloud file hosting service, and create a local bookmarks profile.
A "profile" is a file where your bookmarks data is saved by syncmarx via cloud file storage. By setting up multiple profiles, you can use the same cloud hosting account to store multiple sets of bookmark data (e.g. "Personal", "Work", etc.). These files are tiny and private, so you can save hundreds of bookmarks all under the security and comfort of your own personal file hosting service.
There is still room for improvement, but this free browser extension does an excellent job of keeping bookmarks synced between browsers.
Really good alternative to XMarks, just that you can't see/edit the content on a website as the bookmarks are hosted on your Dropbox account
This one have a great potential to be the Xmark replacement. Still on alpha version, but it is the closest one in my opinion.