Rated 5 out of 5 stars

5-star, but broken again... With addon enabled the header area doesn't show at all, with addon disabled header area with 3 lines appears.

Léirmheas ar leagan níos sine den bhreiseán seo (2.18). 

No headers at all? You possibly clicked "Hide Headers".
Right click a message or the message list and select "Show Headers" near the bottom.