If you're running Chrome please for the love of all that is holy enable Click-To-Play for all plugins. With it disabled it is like running without a pop-up blocker.

You can do so in Settings -> Advanced Settings -> Content Settings -> Plug-Ins -> Click To Play.

When you visit a site which has a plug-in you'll get a UI control similar to the pop-up blocker which allows you to add it to the exceptions list and or to allow it just this one time. You should add YouTube to the exceptions list.