You can fix the white space annoyance of YouTube’s new layout by installing a user scrip called “Youtube Center Aligned”. The script works on Firefox, Chrome, and Opera and can download from UserScripts.com.

Installing YouTube Center Aligned is very simple. Firefox users need to install the Greasemonkey extension before installing the script, and then go here to install the user script. Since Chrome supports Greasemonkey scripts natively, you can install user script without GM. To install, download the user script, and open the Chrome Extension page (Menu > Tools > Extensions) and drag-and-drop the downloaded script inside to install it.

After installing the user script, go to YouTube homage, click on the YouTube Center toggle icon (gear like icon, see screenshot) and check the box “Center Page”. [Via]