+Approach #1 (add-on)
+^^^^^^^^^^^^^^^^^^^^
+
+Install the Toggle Word Wrap add-on that is available from
+https://addons.mozilla.org/thunderbird/addon/toggle-word-wrap/
+It adds a menu entry "Enable Word Wrap" in the composer's "Options" menu
+that you can tick off. Now you can compose the message as you otherwise do
+(cut + paste, 'git format-patch' | 'git imap-send', etc), but you have to
+insert line breaks manually in any text that you type.
+
+Approach #2 (configuration)