Related to this, I think it was unnoticed because at https://searchfox.org/comm-central/rev/753e6d9df9d7b9a989d735b01c8b280eef388bab/mail/components/compose/content/MsgComposeCommands.js#3047 we don't really get a prompt, only the "Cannot call openModalWindow on a hidden window" error.
Related to this, I think it was unnoticed because at https:/ /searchfox. org/comm- central/ rev/753e6d9df9d 7b9a989d735b01c 8b280eef388bab/ mail/components /compose/ content/ MsgComposeComma nds.js# 3047 we don't really get a prompt, only the "Cannot call openModalWindow on a hidden window" error.