Rated 5 out of 5 stars

Invaluable tool for editors! Will be sending a donation next week. Your work on this deserves more than a nominal donation.

And thanks, Jorg, for advising users to use a monospace font in the "Fonts & Encodings" section to enable accurate cursor placement in the HTML Tab. That solved an issue and limitation I'd struggled with!

Searching and replacing junk html (such as inserted when one cuts and pastes text from an MS Word document or a gmail text into an email, for instance) is difficult because the only search/replace available within the HTML Tab is the Thunderbird text-oriented one. The primary problem from a search/replace perspective is that it doesn't recognize and deal gracefully with line feeds.

Another improvement would be to smarten up the Line Wrap setting with an option to condense multiple spaces to 1,2,3, etc. as needed for readability. That would make find/replace much easier.

My current work-around is to copy the whole message html and paste it into an html editor, edit it there, then paste the results back into the email. Works fine, but a native html editor would be a great service. A tall order for an add-on, I imagine.

But you deserve a rich reward for the work you've already done! I don't think I've sent you anything yet. but will within the month. I hope others do too....

This review is for a previous version of the add-on (3.1.11). 

The thing is that the HTML content is processed exclusively by the embedded Ace HTML editor, my add-on is just the glue between it and Thunderbird. So whatever Ace implements will be available.

Other than that I can just suggest to copy/paste the HTML to a tidy program or other HTML editor like you already suggested and copy/paste it back after the clean-up.