Here's the instructions. First, make sure you have completely closed Thunderbird and Firefox (use the menu: File > _EXIT_)
You know that Windows key on the keyboard? The one between the CTRL and the ALT keys at the bottom left on the keyboard.
Well, call that the WIN key and press and hold that key and then hit R. That will show the 'run' dialog. Type %appdata% and hit enter.
Copy the Thunderbird and the Mozilla folders to a temporary storage location like a USB stick or USB harddrive or some such. Then go to the new computer and move those 2 folders to the same location; again do WIN+R and type %appdata% and hit enter. The folder it shows you is the place where you have to dump the Thunderbird and Mozilla folders.
Then simply go to http://www.mozilla.com/ and download and install Mozilla Firefox. All your settings will be preserved.
For Thunderbird go to http://www.getthunderbird.com/ and download and install Mozilla Thunderbird. All your settings will be preserved.
Step 3: Profit?