I edited my YouTube cookie about a year ago and I'm still getting the old layout. This may not last for long. I'll deal with the new layout when the cookie edit goes away.
Edit Cookie for YouTube's Old Layout:
https://www.youtube.com/watch?v=qeAgxcM9tIk
1. Set permissions (Page Info Window) in PM to "Allow" cookies at YouTube.
2. Open the Web Developer Inspector Tool by pressing F12.
3. Click on the "Gear" Toolbox Options button in the upper right corner.
4. Check the "Storage" box under Default Developer Tools.
5. Click on the Storage button in the toolbar.
6. Go to the YouTube site in the browser.
7. Click on Cookies in the left column of the Inspector
8. Click on the YouTube cookie.
9. Select the "PREF" cookie in the Name column.
10. Double click the line in the Value window.
11. Paste either &f6=43418 or &f6=8 after f1=50000000
Example: f1=50000000&f6=43418
12. Click on the "Gear" Toolbox Options button in the upper right corner.
13. Uncheck the "Storage" box under Default Developer Tools.
14. Close the Web Developer Inspector Tool.
15. Set permissions in PM to "Use Default" for cookies at YouTube.