andreip@posteo.net is a firefox accounts account. The place to manage the email is at http://accounts.firefox.com/ - however, I believe it does not currently support changing the primary email.
note: keep in mind that several RP (relying parties/websites) may use your email as your identity, thus changing primary email may break access to these RPs.
Yeah the flow is pretty confusing here (aka it’s broken), you’ve actually got to make sure the email you want to change to in Discourse isn’t a secondary email, otherwise Discourse will complain about you changing your email to an email which already exists… apologies!
I’ll manually change your primary email server-side.
Edit: emails updated. Let me know if you have any further problems!