Rated 5 out of 5 stars

by alta88 on Sept. 30, 2013 · permalink

This functionality may be created by installing userChromeJS from:
http://userchromejs.mozdev.org/

Add this code to the [profile]/chrome/userChrome.js file:

/* Compose window */
if (location == "chrome://messenger/content/messengercompose/messengercompose.xul") {
// Skip blank subject check in MsgComposeCommands.js.
eval("GenericSendMessage = " + GenericSendMessage.toString().replace(/subject == ""/, "subject == null"));
// Skip confirm cancel in MsgComposeCommands.js.
ComposeCanClose = function() { return true; };
}