I often watch video in one browser window while carrying on surfing or working in others. I seem to spend a lot of time trying to resize the window around the video perfectly, so as not to waste screen real-estate and to hide clutter surrounding it on its web page.
I made this extension to solve the problem. It scans through all objects on the page looking for things that might be video, and chooses the largest. Then it resizes the browser window perfectly around it. A small button then appears in another tiny window which can be clicked to restore the browser to its original state.
I hope other people might find this useful, I do!