Hi lukeba, Thank you for your question, this is odd. The feature in the sync settings is unchecked as well? Is there a preference that stores form data? That may be attributing to this.

"services.sync.pref" search for on the about:config page to see if there is one listed there. (formfill.enable? )

I hope this helps.

In sync settings I've checked all options: just the password sync is not enabled. formfill.enable is enabled, but it should not affect syncronized data.

Were they synced before? I wonder if they were selected if they would store once synced once to that profile.

If you go to the password manager Options > Security > Passwords "Saved Passwords" and remove any passwords that should not be there. After the next sync, is that data still there?

Wait a moment: I'm talking about synced username, not their passwords. I don't want that these informations (username) would synced.

Ah, my apologies. A past solution to this was to delete an old autocomplete synced entry: http://kb.mozillazine.org/Deleting_autocomplete_entries