Fortunately, Mozilla Thunderbird is not stubborn about this. Instead of moving the cursor up every time, change Mozilla Thunderbird's mind just once — for all future replies to start right at the top, above all quoted text by default.
Start Your Reply on Top in Mozilla Thunderbird
To make Mozilla Thunderbird position the cursor on top, above quoted text when you reply:
- Select Tools | Account Settings... from the menu.
- Go to the Composition & Addressing category under the desired email accounts.
- Make sure Automatically quote the original message when replying is checked under Composition.
- Now choose start my reply above the quote next to Then,.
- For lazy top-post quoting, you may also want to choose below my reply (above the quote) following and place my signature.
- Click OK.

