twitch.tv, some scrollbars scroll, others do not

[mortalwombat]

Twitch TV (livestreaming) website uses some non-standard scrollbars that do not work with latest Pale Moon, although they do work with another browser like latest Mozilla. Win 7 Ultimate 64-bit. Pale Moon 27.7.2 32-bit.
for example on this page, or any livestream page: https://www.twitch.tv/mitchflowerpower
the central part of the page scrolls up and down, with a non-standard scrollbar on the right, just fine. the chat sidebar has its own non-standard scrollbar that also scrolls up and down. but when clicking the smiley face next to "Send a message" near bottom right of page, that brings up a "Sub Emotes" section with another up and down custom scrollbar, similar to the other 2 working ones, and this one does not scroll. it is stuck. page source code is many kilobytes all on one line, so it is has been difficult to check.