Hi!

Are you following the steps described in the following article?

How do I add a device to Firefox Sync?

Can you tell me exactly in which steps is it failing? Are you getting the 12 character code and adding it to your computer? Do you have a Beta version of Firefox in the mobile? If so, make sure that you uninstall it.

If you can give me exact steps, I can try to figure out if it's a bug or something is failing in the process.

Sorry, I forgot to mention that I am using a custom sync server. I click below the 12 character code on "advanced setup", check "use own server", enter all of my details and hit "connect" afterwards. But Firefox doesn't even try to connect to the server I entered (I can see that in the server logs) but immediately displays the error message "wrong recovery key".

And as I said, the entered data is definitely correct and works perfectly with Firefox Home.

Sorry for the late reply,

Have you tried to look into the Sync Log in the client side? It seems that there's a problem with the communication, even before it starts. The following link explains how to check the logs and how to open a bug if something doesn't look quite right: https://philikon.wordpress.com/2011/06/13/how-to-file-a-good-sync-bug/

Opening "about:sync-log" in Firefox mobile results in an error.