Here is a HTML5-Gtk Player, which I released together with PostX 0.4.2. It plays Youtube and HTML5 with Python. Note. The dependencies listed below might be different depending upon your system version or Linux distribution.

#HTML-GTK PLAYER Copyright (c) 2017 JJ Posti <techtimejourney.net>
#This program comes with ABSOLUTELY NO WARRANTY;
#for details see: http://www.gnu.org/copyleft/gpl.html.
#This is free software, and you are welcome to redistribute it under
#GPL Version 2, June 1991″)

4th of March 2018:

HTML-GTK Player v.4 is added This release fixes some bugs.

11th of September 2017:

HTML-GTK Player v.3 is added. This release fixes HTML5 rendering issues on Youtube. Continue reading →