I have found a little something that will help the viewing quality and speed. I often wondered why everybody was posting video on youtube in 60fps until now. I never really cared too much as 480 actually does have decent quality by today's standard compared to a few years ago. But it turns out that the whole slow video nonsense is an attempt to push people to use the chrome browser since youtube is now owned by google. What I have found that seems to work quite well for the Firefox and apparently Safari browser users, is a little browser addon called Greasemonkey...
homepage --->
http://www.greasespot.net/)
...install this either by going to their page or in Mozilla Firefox, just go to your addons section under tools and do a search for it, install from there. After installing, go to this site to install the script...found here...
https://greasyfork.org/en/scripts/23329-disable-youtube-60-fps-force-30-fps
This script (which has a green install button) will get automatically picked up by Greasemonkey and installed, this will disable the HDxxxx60fps only option and get the good ol 30fps HD back. It works well on older hardware too and can be disabled anytime with ease. But make sure you reload the page after you enable the Greasemonkey and set it to disable 60fps. This setting can be found at the bottom of the Greasemonkey drop down menu. For me, it works well because I don't need the fastest internet service available but I do appreciate being able to watch HD videos the way I used to, without massive lag, and now I do again