... As it turns out, your "friends" over at Microsoft must be really liking your posts and the "new ideas" presented to them (just joking, of course! ) ...
So they thought: Matt did mention that "downloading new releases still works (for now)", so let's just scratch that! () Hence:
https://forum.palemoon.org/viewtopic.php?f=70&t=28849 (do click, it's safe )
which, in turn, necessitated
https://github.com/martok/palefill/issues/47 and
https://github.com/martok/palefill/commit/3a480ab
TL;DR: Assets (under Releases) have been hidden behind a WebComponents-requiring "wizard", thus fresh installs of UXP-based browsers are unable to access, among anything else released in GitHub, the very one (two, if you count gh-wc-pf) extension that would make them GitHub compatible ... Fortunately, workarounds are available...
In retrospect, that was a smart thing to do! Comment attachments are accessible by UXP-based browsers without palefill or gh-wc-pf...