Rated 1 out of 5 stars
This *was* a great (five-star) extension that added useful capability to Thunderbird. Unfortunately, Thunderbird's UI changes broke the extension, and the author says they're not continuing development. So even though the extension shows as compatible with, and will install on current versions of Thunderbird, it doesn't work. My one-star rating only reflects the fact that the extension doesn't work anymore, and is NOT intended to reflect on the quality of the author's work.
Thanks jmozmoz for years of work on this great extension! I totally understand your desire to move on to other things, and really appreciate having been able to use the extension for years.
I have no idee, why you can install the addon/use it with Thunderbird 69 or newer. I set the compatible version to 69.01a1 (before) and now 68.*. This seems to be a bug of Thunderbird itself.
I checked it now, and CompactHeader is shown as non-compatible.