There are 3 things which I am working on... two are able to be committed now, but was trying to fix all three before making a set of commits/patches:
_pthread_self() undefined in jemalloc.c
In the DARWIN section I just #define _pthread_self() pthread_self() which seems to be the correct fix based on updated jemalloc.c code in Mozilla and other sources.
Add OnBigSurOrLater() to nsCocoaFeatures.h/mm and add sections in the theme to draw things that match the 11.0 Big Sur look and feel.
Fix popup menus not drawing correctly. Almost all popup/dropdown menus in Pale Moon fail to draw correctly... the text and separators are all missing. However the highlight color appears when you move the mouse over them and clicking them works properly, you just can’t see the text to know what you are clicking on.
Comparing to the behavior in Basilisk, the popups in Australis that are more complicated render properly, like the search field and the menu button, function properly but the more basic menus when you secondary/right click on a page appear blank like in Pale Moon.
It is clear that it is drawing the menus itself, and not using native menus. In nsNativeThemeCocoa.mm there are methods to draw the menu background and highlight which appears to be working as expected, it is just the menu text and separators that are missing, but I haven’t yet identified where in the code this is (or should be) happening.