I want to thank you for this! This way it's way better than a double-click feature, which is very unusual on websites.
I just have one question, I applied step 3 also, but this also creates an extra Reply-"button" to a PM. So, now you have two options under a PM, "Reply" and "Reply to PM"... of course the first one isn't working, but it's confusing. How can we get rid of this extra "button" in a PM, but retain it under "normal" posts. Added an attachment for clarity.