>>252

1) Install an extension that allows you to easily apply custom style rules to web pages. For example, Stylus:

https://addons.mozilla.org/firefox/addon/styl-us/

(2) Then install this custom style rule I posted last night to restore the scroll bar:

https://userstyles.org/styles/157633/youtube-left-column-scrollable-march-2018

ふたつのアドオンいれたらOK
ありがとう