[Firefox] Utilise CSS rules to fix hiding the native scroll bar in the channel list (most noticeable on servers with banner images above the channels)

Illustrative image of the change:

CSS: (As used as a user style over ride, obviously you can remove the !importants and not set a BG colour)

.scrollerWrapPolyfill-DBQCMm .scroller-2FKFPG {
scrollbar-width: none !important;
}
.scrollerWrapPolyfill-DBQCMm .scrollbar-2rkZSL, .scrollerWrapPolyfill-DBQCMm .pad-29zQak {
background-color: transparent !important;
}

You can read about the scrollbar-width rule here: https://developer.mozilla.org/en-US/docs/Web/CSS/scrollbar-width

This has the nice bonus of recovering the remaining width from the channel list, from the hidden scrollbar.