You can still view YouTube if you use the previous version of ViewTube
Greasemonkey script and set the user agent to an older version of Firefox
(this one should work):
Mozilla/5.0 (X11; Linux i686; rv:43.0) Gecko/20100101 Firefox/43.0
(you can do this via the User Agent Switcher add-on or by setting the user
agent in general.useragent.override via about:config).
Here is the previous version of ViewTube:
https://raw.githubusercontent.com/sebaro/ViewTube/531c2224b05fc92bef6dd9e1a4a2f0d03da8bbcd/viewtube.user.js
(You should disable updates in the Greasemonkey settings for this script as
the newer version no longer works.)
