Some things just bug me. One of them is when I have to scroll to the bottom of a mesasge to see what someone wrote. Unfortunately, this is the defaul setting in Thunderbird for how to reply to someone’s message. To change that, and stop driving me crazy, here’s what you need to do:
- Go to Tools > Account Settings.
- Under the account you want to change, go to the Composition& Addressing section.
- The second checkbox says “Automatically quote the original message when replying” and has a drop menu underneath it. Change that menu to say “start my reply above the quote”.
This will put your response above someone’s email rather than below. If you prefer the other setting, then God help you cause you drive me crazy.
Posted by Slushman 
The unofficial how-to blog for Thunderbird 