Another way is to install the development version of ViewTube. Indeed
https://raw.githubusercontent.com/sebaro/ViewTube/master/CHANGES says:
#2017.09.02
- fixes YouTube for both designs
#2017.09.01
- fixes YouTube for new design
To install the development versions of ViewTube and ViewTubePlus, you first
need
https://addons.mozilla.org/firefox/downloads/latest/greasemonkey/addon-748-latest.xpi
(GreaseMonkey) and then to click on:
https://github.com/sebaro/ViewTube/raw/master/viewtube.user.js
https://github.com/sebaro/ViewTube/raw/master/viewtubeplus.user.js
