Comment 28 for bug 52667

The problem with tying it to the "Reply" button is that you lose the "Reply to
poster" functionality which currently exists on lists which don't mangle the
Reply-To header but do add a Mail-Followup-To (or other supported) header.

Reply-To-All isn't entirely correct either unless you include other addresses in
the TO and CC fields, since the message may have been addressed to a mailing
list as well as other recipients.

I don't think there is any way around a "Reply-to-list" button without losing
some current functionality. Whether or not loss of current functionality is
acceptable or not is not my decision, but I'm not seeing the issue with another
button since the functionality provided is different from any of the current
buttons.