Rated 5 out of 5 stars
UPDATE: developer has been great about looking into the problem mentioned below - including discovering a bug in Compactheader & reporting it to that extension's dev. He reports that the latest version of Toggle Headers includes a workaround. I haven't tried it yet, but I'm revising my review score to reflect that TH is super useful in combination with CH, when that relationship is working - and that the dev (mattsch) is very responsive to comments.
This was a terrific add-on, but it doesn't work properly with Compactheader 2.0.10... Hitting "H" used to expand the headers pane as advertised, now it just blanks the pane out. Hitting "H" twice will expand the pane, but the previous setting isn't remembered, so you have to manually collapse it again.
Compactheader 2.0.10 is required for newer versions of Thunderbird - so basically, Toggle Headers hasn't been updated, and now doesn't completely work as advertised with newer (38+) versions of TBird.
Thanks for letting me know about this problem, meeotch1.
I am looking into this problem and hope to release an updated version soon, which is compatible with CompactHeaders 2.1.0.