I wish people differentiate various web based bookmark services from actual browser bookmark synchronizers.
After xmarks' demise it was really hard to find correct replacement due to the above. I want to use native bookmarks in my browser instantly including locator search etc.
I ended up using awesome xBrowserSync which has cross firefox/chrome extensions to sync bookmarks. I self host with excellent and compact https://github.com/ishani/xSyn server written in go. Though you could use public servers as it's client side encrypted and anonymous.