There is an icon in the lower right corner that appears once the video loads and starts to play. If you click quickly--immediately right after the video loads--it will flip to full screen without having a pop-up. If you wait too long to expand to full screen, a pop-up comes in a new tab. Close the tab and then reclick the "expand screen" icon. Once the video is full screen, you can pause it, fast forward, etc without having to deal with pop-ups. I have never had a problem with the pop-ups adding malware, viruses, etc.

Once you click it you might get a pop up taking you somewhere else- close it go back click again. Do it till it expands

There will be a enlarge button... click it