Great! A candidate for the main program... Rated 5 out of 5 stars
Finally I found this add-on - now I can choose header-size again!
I hadn't imagined there to be an addon now for this purpose. Several months I had been irritated, that Thunderbird had lost the ability to reduce header-size - uncomfortable especially on a netbook, where space is scarce.
Now I understand, there was a change that meant to increase functionality...
I think, this functionality is really important. I strongly encourage it being re-integrated into the main program!