You would want to check the author's support website, show in tools > add-ons > management, and linked from the Thunderbird add-ons website.

are there no other add-ons for auto correct?

Autocorrect what? I think is the issue. I use the Grammar and Spell Checker but it does not automatically change anything https://addons.thunderbird.net/en-US/thunderbird/addon/grammar-and-spell-checker/

I can not find anything in the addon library that matches autocorrect https://addons.thunderbird.net/en-US/thunderbird/search/?q=autocorrect&appver=&platform=

I would really love a learning function for an auto correct feature. It used to be there years ago but was lost. Every body knows the typical typos like" hte" = the "htanks" = thanks "ebst" = Best and so on. "I fthere" would be "afunction" where one could type in his typical typos to be learned by Thunderbird to auto correct these nasty ever recurring typos.

I believe this is a very common problem and a simple solution would be much appreciated, instead of going piece by piece through the spell checker.

"Thnak" you Folks for giving this some thoughts.