STR: Attach a BMO message which has CTE quoted-printable to a message and send. Result 1: message/rfc822 attachment looks good in the preview pane. Compose a new message and drag the message/rfc822 attachment to the attachment bucket. Send message. Result 2: message/rfc822 attachment looks garbled. Analysis: The message/rfc822 attachment maintains these headers: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable However, the content is not encoded quoted-printable as originally, but instead 7bit (at least for ASCII messages from BMO). So any = sign in the message body will lead to a decoding error since an attempt to decode the message from quoted-printable is made. === Sadly when reporting this bug I noticed another bug: Double-clicking onto the attachment which has been dragged from a previous message crashes: https://crash-stats.mozilla.com/report/index/bp-e49fbf9b-7fc3-4024-8fa7-243512170301 https://crash-stats.mozilla.com/report/index/bp-aa5a6b84-2661-47b8-8365-efd0c2170301 That's apparently covered in bug 1316416.

Fixed by bug 1350080.

This has got nothing to do with the crash in bug 1316416. Bug 1343536, which has similar steps to reproduce, can create the crash of bug 1316416.