Size of video window small

The size of the video playback window is small most of the time. Sometimes, at random, the video will fill the browser. Is there any way to have the playback window fill the browser by default?

Thanks for all the help. Isn’t anybody there?

On the lower right hand corner of the video there is a box that expands the screen with a click. To minimize the video again, just press escape.

Thanks, I already knew that. Sometimes the video would fill the browser window, not the whole screen. It mostly happened on some of the earlier videos.