Rated 5 out of 5 stars

per Peter Passchier el set. 6, 2022 ·

Used this for years, but it recently stopped working properly -- I thought. But it is possible to select Hide Headers when right-clicking on a message in the list, which will hide the whole bar. I had inadvertedly done that. But this is quickly restored by consecutively selecting Show Headers..! So the Compact Headers addon is still the only one of its kind, and it keeps working, and @Dillinger responds to reviews, which is great!

This review is for a previous version of the add-on (3.0). 

per Dillinger (desenvolupador) a set. 11, 2022 ·

If it doesn't show any headers at all, you possibly clicked "Hide Headers".
Try right clicking a message or the message list and select "Show Headers"
near the bottom.