Because of this extension, youtube videos fail to start, and if they do start, they stop when I go forward. When i disable this extension the issue goes away.

Not very effective at masking. "whatismybrowser" will still pick up that the browser "looks like firefox"; and so will many other sites.

Here it does nothing. For instance, on Google search (www.google.com) using Chrome we have that "Search Labs" option/icon up on the right of the page. Using Firefox we don't see that, even enlabling this extension to act on that page.