As YouTube’s home page is now left aligned, on wide screens it results lot of blank space at the right. If you hate this, you can fix this issue by installing “Youtube Center Aligned” user script on your browser.
Youtube Center Aligned user scrip works on Firefox, Chrome, and easy to implement. To install the script, go to Userscript.com and download it.
For Firefox, you have Greasemonkey extension installed on your browser to install Youtube Center Aligned” user script. So, first install GM script and then install the user script.
For Chrome (also Opera), you don’t need Greasemonkey to install the user script. 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 – techtrickz.com)