I recall in the past lots of people reporting issues with their bookmarks going missing with xBrowserSync. It also hasn't been updated in quite some time. My biggest issue, is it appeared to primarily integrate with the browsers bookmark manager... and once you had thousands of bookmarks in the browser bookmark manager, it started lagging. I prefer something with a native local service to search and manage bookmarks, like Shiori.. but I don't like Shiori all that much either.