The update on their news post supports the "don’t sue us for sending the data you asked us to send" intention.
UPDATE: We’ve seen a little confusion about the language regarding licenses, so we want to clear that up. We need a license to allow us to make some of the basic functionality of Firefox possible. Without it, we couldn’t use information typed into Firefox, for example. It does NOT give us ownership of your data or a right to use it for anything other than what is described in the Privacy Notice.
Whether or not to believe them is up to you.
Whether the terms are abusable by design or by accident doesn't really matter, you get is abuse either way.
How I wish we could have some nice things sometimes.