This is actually based on the Goanna web engine (a fork of the Firefox / Gecko web engine) derived from the https://www.basilisk-browser.org/ . You can find out more here - https://forum.palemoon.org/viewtopic.php?f=69&p=275829#p2758... .
The same complaint in my original comment applies - at what version was it forked from, what version of Firefox is it equivalent to?
https://www.basilisk-browser.org/features.html
Basilisk supports the technologies required for the modern web, while deliberately avoiding the rapid architectural and interface changes common in mainstream browsers.
Nothing but very vague and useless marketing-speak.
Ah, that explains why there is still NPAPI plugin support.