I thought this would be easy, but turns out it's not. I need to set the Firefox viewport size to a given value (larger than my screen resolution). What I want is not to enlarge the application window, but to enlarge the size available to the html content. The viewport won't be physically larger, but will "tell" the html that it is, so that webpages will take more space (obviously making scrollbars visible).

For example, let's say my physical Firefox window is 800x600 px. I'd like to set "viewport size=2", then the available space for the html to render would be 1600x1200.

Web Developer has a resize feature but it doesn't work when you set a size larger than your screen resolution (in Windows 7).

Thanks in advance (I hope my explanation makes some sense).