Browser specific syncing
Browsers Firefox and Google Chrome both offer their own default solutions to syncing bookmarks. Firefox Sync can be used to sync not only bookmarks but passwords and browser history across different Firefox browsers including Firefox for mobile devices. If you have a Google Account you can sign in to Google Chrome to sync bookmarks, extensions, themes and browser preferences.
Update (May 7, 2018): Xmarks has been discontinued so this is no longer a viable alternative