Rated 5 out of 5 stars

This works great. But: unlike the way it's mentioned in the text, it does not revert to the default setting when moving on to the next message. Indeed, instead it changes the default setting to whatever you select via this add-on - you can then easily set it back, however. Tried this with latest version of TBird (60.5.x) on both Mac and Windows. Would be nice if it worked that way, but no stars removed. Thanks for this!!!

This review is for a previous version of the add-on (5.4.3). 

Mabe you should read the description on my website:
https://www.thunderbird-mail.de/lexicon/entry/226-allow-html-temp-add-on-to-allow-html-only-temporarily/