How to Create an Email Signature in Thunderbird

Step One: Create an HTML signature file:
Using your favorite html editor, create an html document with your desired signature information.

Save the file

Step Two: Add signature file in Thunderbird

Tools >> Account Setting
Pick the identity you want to add a Signature to
Check box that reads: Attach This signature.
Then choose the file we created prior.
Click OK
Try composing an email and see if your new signature appears