This is a Firefox XPI extension that adds extra height to the window so content can be scrolled to the middle of your monitor.
To build the project, install the cfx tool first. Then run 'cfx xpi' from the root of this repo.
The file structure of this project is a modified version of the sample extension created by 'cfx init'. I changed the lib/main.js file to use the PageMods API instead of the Tabs API.
Tested on Firefox 26.