Puntuado con 5 de 5 estrellas
To those having problems. You need to update to 4.2.3. All updates to addons must be reviewed by the Mozilla addon team before being released and they haven't gotten their lazy butts to do it for version 4.2.3 even though Xmarks submitted the updates months ago and Xmarks is one of top addons.
You need to either download xmarks directly form the official xmarks site or go into the development channel on this page to get the properly working version.