Have you set view / headers to normal?

Thank you for your quick response. Yes, I do have the headers set to normal. I also clicked "compact" in that same pop-up menu - made no difference. If all that stuff were just singled spaced instead of double-spaced, that would solve most of the problem.

this is my header. any different than yours?

Yes, it looks the same as that.

I'm afraid that's standard. You could try view/layout/vertical view and adjust the with of each view.

You have the add on Compact Headers installed. The choice of Compact under Headers is not default to Thunderbird and it comes with the add on. You have updated Thunderbird and the old Compact Headers is no longer compatible. Go to the add on page and get the new version of Compact Headers if you want to continue using it.

Airmail, there is no Compact Headers add-on that I can find at Mozilla, at least for the new version. There's something called Compact Menu, but that doesn't seem to do anything like Compact Headers did. Is it called something else or do you know for sure there's a Compact Headers add-on for 38.0? Thanks for your help (and yours, too, Gnospen).

You mean like this one?

https://addons.mozilla.org/en-US/thunderbird/addon/compactheader/?src=hp-dl-featured

I believe that's the one you told me was not compatible with the updated Thunderbird. The description says it's for version 36 and older. I can't find anything comparable for 38.0.

I went ahead and deleted the old add-on, just to keep things tidy, and oddly enough, my headers reverted to normal. Or, at least the little +/- button in the upper left corner of the header returned so I could get rid of everything but the subject line, so I'm good now. Thanks!

If you bothered to follow the link you would see that it says works with versions 37 - 40. At least on my computer.

If you are back working I will go back to ignoring this thread.

I apologize, Airmail. I read "For Thunderbird 36 and older" and just quit reading after that. Thanks again for your assistance.