This should work on Google Chrome, Firefox, Microsoft Internet Explorer, Opera, and Apple Safari. If you know how to make it work on mobile devices please leave instructions in the comments below.
1.) Open your favorite web browser from the list above and go to https://www.youtube.com/html5
It should look like this:
2.) Click the blue rectangular button. This will change your default player to the HTML5 player that has the settings button to allow you to chose your video’s speed. You will not have to visit this page again unless you are on a different browser or using a different computer.
3.) Now whenever you view a You Tube Video you can use the cog setting icon (circled in purple in the picture) to adjust the speed as you like for that video. The speed will revert to normal with each different video. You will have to click the cog icon with each video to change the speed.