Well here is an interesting question. If FEBE the “Firefox Environment Backup Extension” can support Box.Net, then why not Ubuntu One? For that matter, why is there no Ubuntu One or DropBox extension for Firefox? Maybe there already is, I’ll do a little more research and see what pops up. In the meantime, you can install FEBE
UPDATE: I just received news that as of today, 4-04-2010, Ubuntu One will have a Firebox Bookmarks synch facility. A step in the right direction.