Inside the browser, from these 2 sites http://www.webupd8.org/2014/01/enabl...in-chrome.html, https://wiki.archlinux.org/index.php/Firefox/Tweaks
I tend to install Chrome mainly so I can play with Netflix, although I hear FF can supposedly do it in Linux as well now. Never did get lightbox working, gave up on that entirely.

Not everything is showing as enabled after forcing, but it's definitely better. I compared system resources to a near identical machine running chrome on windows 10 while playing the same 1080P video on youtube, Linux used about the same CPU % after the tweak but half the RAM. Before the tweak it was nearly double - CPU 25-30% with tweaks, 45-60% without - and occasional spikes higher