If you have problems with current Shockwave Flash plugin versions then check this:

• see if there are updates for your graphics drive drivers

https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)

https://forums.adobe.com/message/4468493#TemporaryWorkaround

• disable hardware acceleration in the Flash plugin

https://forums.adobe.com/thread/891337 See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

As stated, I am currently not experiencing problems with Flash players. Just the HTML5 one that Youtube is using.

Check for updates for your graphics using the above.

My graphic drivers currently has the latest updates installed to them. I'm using Geforce Experience to look for and install the latest drivers for my graphics card.

Disabling protected mode didn't solve it, since it's not Flash that I'm having problems with.

I can't choose to disable hardware acceleration, since those instructions are for Flash, and there is no such option for HTML5 as far as I know.

You can try to disable hardware acceleration in Firefox.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

You need to close and restart Firefox after toggling this setting.

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes
• https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

I have it already disabled, to solve a previous issue I had. https://support.mozilla.org/en-US/questions/1059207

I found what the problem was. On the quality settings for each Youtube video, whenever I have "Auto" on, and try watching it fullscreen, then it has low framerate.

But when I manually select the quality, and fullscreen it, then it's just as good as not having it fullscreen.

Okay, it's only with bad framerate when the quality is anything but 1080p. But when it's 1080p, there is no problem with it.

I'm still having the same problems, not only with Youtube, but also with Twitch switching over from Flash to HTML5. Except on Twitch, the framerate is consistently low, and sometimes stutters.

Hey, i' ve had the same problem when youtube changed to HTML5. I've found this solution working: go to about:config, then find the option media.webm.intel_decoder.enabled and set it to true. I have no clue what is that option and why is it disabled by default, but it worked.

cepir said

Hey, i' ve had the same problem when youtube changed to HTML5. I've found this solution working: go to about:config, then find the option media.webm.intel_decoder.enabled and set it to true. I have no clue what is that option and why is it disabled by default, but it worked.

I don't have this option.