You can go to Tools -> Options -> Advanced -> General -> Config Editor, filter on the pref mail.operate_on_msgs_in_collapsed_threads and toggle it to false. That way not all messages are opened, but only the top one. If you want to change the behavior of the Enter key, you might have luck with the keyconfig add-on, which can be downloaded from here: http://mozilla.dorando.at/

Thanks, I have set "operate_on_msgs_in_collapsed_threads" to false, and when I press enter on collapsed thread, indeed only the first message is opened. This is a big improvement, but still not perfect.

I have the keyconfig extension, and have set "Expand All Threads [Threads] to ENTER, but that has no effect. Enter still opens the first message in the thread.

do you have any other idea how to either: 1) do nothing when ENTER is pressed on collapsed thread 2) or (preferably) un-colapse the thread

?

actually, this is not a solution at all. I just noticed, when "operate_on_msgs_in_collapsed_threads" is set to false, I cannot delete whole thread. I have threads containing tens of emails. I need to delete whole thread at once, not deleting 70 emails individually.

I admit it's hardly a workaround...

If you want to remove all messages in a thread, you can first select them by pressing Ctrl+Shift+A and than delete them.

Be sure though that you don't press Ctrl+A, because then you select all your messages, not only the ones in the current thread, and you prolly won't want to delete them :-/