Very useful!

A few suggestions:
1.) Add a keyboard shortcut
2.) Add options for putting the popup on the left or right side of the screen -- not just in the corners. I use this extension most when I want to view web pages side-by-side, at full height.
3.) Express popup height/width options not in pixels but in fractions of a full screen. This would make the extension work consistently across monitors with different pixel resolutions, and across different machines.