Make sure you are signed in with the same Firefox account and that bookmark syncing is turned on for both mobile and desktop. If the issue still persists, sign out of your Firefox account and sign back in, making sure that bookmark syncing is enabled.

All done. I even deleted the history and cache on both devices without success. Syncing isn’t working.

Assuming you have connected the same Sync account on both your mobile and desktop copies of Firefox:

In Firefox on your mobile device:

1. Go into the Settings menu and select Firefox Account.
2. Tap on Synchronise now.

This will “force” a synchronisation of the data that is on the local device storage. Do this on the device with the most up to date bookmarks and then do it on the device with the most out of date.

Unfortunately, this doesn’t solve the syncing issue as well. At the moment the desktop browser is the most up to date and the iPhone app is not. Nothing is syncing anymore.

I just signed out and uninstalled Firefox on both devices. After reinstalling it the browser is syncing again. Weird. Thank you for your efforts and help!