It was a work-in-progress tree and they weren't redistributing any binaries/sources from there. The Pale Moon devs were both wrong and remarkably hostile.
Additionally, (pardon me if I misunderstood) the Pale Moon developers consider it “normal free software development practices” to bundle libraries with an application and use them instead of the system ones? This seems to be the opposite of how most software libraries and prevents browser libraries from being updated as usual through the package manager.
This is purely a trademark dispute. They want you to rename the browser if you deviate from their franken-patchset of firefox + all the other weird old libraries they use. Such a thing would obviously not fly in a security focussed OS like openbsd (or any OS for that matter). So you can rename the browser if an agreement is not reached, which is fine. The issue, however, is that these guys are so protective of their name (really, who even has heard of it?), that they thwarted a WIP attempt by someone to port this mess before the ported product even saw the light of the day.
The astonishing thing to me is that, as mentioned elsewhere, this mess in the GitHub issue happened after the person doing the port politely asked the Pale Moon people about the right way to do things with regards to patches and branding: https://forum.palemoon.org/viewtopic.php?t=18256