Safari 8 (Yosemite): Block pop-ups and unnecessary content
You can prevent webpages from displaying pop-up windows or loading time-consuming content that may be unnecessary. However, blocking pop-ups and unnecessary content might also block some content you want to see, or features like animation.
Choose Safari > Preferences, then click Security.
Select “Block pop-up windows,” then deselect Allow WebGL and Allow Plug-ins.