https://github.com/WaterfoxCo/Waterfox/commit/8e55e434750190f1e5b07e48d097aace326e6270#diff-3aff55c0107bc01ea0acc95c89ad2a717976cfdde5f717aa2c5f858fde12557f

--- Waterfox-2021.09-classic/config/system-headers
+++ Waterfox-2021.09-classic/config/system-headers
@@ -1335,6 +1335,7 @@
 unicode/udatpg.h
 unicode/udisplaycontext.h
 unicode/uenum.h
+unicode/uniset.h
 unicode/unistr.h
 unicode/unorm.h
 unicode/unum.h