A) You are completely dismissing that SteemConnect is not working either.
B) Keychain works for every other proposal vote on the page, except the return proposal.

Could you perhaps look into the possibility that maybe I'm trying to report a legitimate bug here and not looking for general support?

EDIT: Chrome (latest) has the exact same issues as Firefox. No popup appears when attempting to vote for the return proposal via SteemConnect or Keychain