The limit of synced bookmarks is 5k for a mobile device. However these are some troubleshooting steps that you can take for syncing: # In the Firefox Account listed in the Android Settings, doe the sync give an error for the need os auto data to be enabled? # Are there any error messaged when you detach the account and reconnect the account? #Are cookies enabled in the mobile device Firefox settings? # Are all devices logged in at accounts.firefox.com? I hope this helps.