+++ This bug was initially created as a clone of Bug #1834664 +++

Selected text from unrelated message is quoted when right-click replying to another message, cunningly with correct attribution line.

See bug 1818683 comment #7 for prior discussion on this.

I also noticed that when you have two messages with a bad charset, repairing the encoding on the first message also forces a repair on the second message when replying to it via right-click. So the autodetectCharset setting is carried over from the viewed message to the message being replied to. Not necessarily strictly harmful, but also not correct in case the repair of the second message is undesired or faulty.

The issue with the charset detection could be fixed at the same location?

let selection;
if (!mailContextMenu.selectionIsOverridden) {
  selection = messagePaneBrowser?.contentWindow?.getSelection();
} else {
  // If overridden, don't force charset detection.
  autodetectCharset = false;
}

Pushed by geoff@darktrojan.net:
https://hg.mozilla.org/comm-central/rev/cf9bc3c16765
Quote the right message when replying from the context menu. r=aleca