How to fix plain text signature when composing message
Installed Enigmail, signature block turned to plain text, so I deleted Enigmail from my account, but signature block is still in plain text even with HTML box checked. What am I missing?
Opaite Mbohovái (2)
I've never witnessed Enigmail actually editing existing text. It will clean up on the fly, but I don't know how it would access the stored signature.
Your signature is in Account Settings? Mine are in discrete HTML-formatted files (I use Signature Switch) and that perhaps preserves the original source of the signature.
Enigmail switches messages composition to plain text, because encryption doesn't work well with inline PGP. You need to turn HTML composition back on. Also see https://support.mozilla.org/en-US/questions/1095191#answer-808980