There is use outside of Web Dev Rated 4 out of 5 stars

Aside from pop up ads and flashing banners, few things are more annoying to me than a page that resizes my main window. Occasionally someone will violate the rules of good sense and web design and resizes the main window without warning you (good sense and web design suggests that if a site resizes your window, it should first spawn a new window with the dimensions that the designers want). I mean having a page full screen is nice, but I kind of like to be able to see things like my IM windows (the "IM windows always on top" option is frequently more trouble than it's worth in my case) and my taskbar. By being able to save your favorite size, you can quickly undo what the poor sense of a bad web designer did.

This review is for a previous version of the add-on (0.57).