What you need:
*Internet explorer 8
*An internet connection :D
*A FREE runescape account (if you already have a members account, then just use the full screen option, duh!)
This method involves using the zoom function in internet explorer 8. This only works on Runescape, not other funorb games.
Step 1: Get the Browser
Download Internet Explorer HERE: www.microsoft.com/windows/internet-explorer/default.aspx
Step 2: Make Your Way to the Game
Step 3: Internet Explorer-Side Modifications
First, Switch your shiny new browser to full screen mode by clicking Tools>Full Screen, or just press F11...
Next, go to the little magnifying glass down at the right hand corner of your screen, click the arrow, then custom zoom. Set it to 140 and hit enter and close the zoomo box windo.
Finally, scroll almost all the way down using the scroll bar (see picture)
Step 4: Runescape Side Modifications
Open the options Tab by clicking on the Hammer & wrench icon.
Under Display Mode, select one that works on your computer and internet connection. I use Standard.
Under Screen Sizing, select RESIZABLE. This resizes runescape with the browser, which is why this workaround works.
Under Advanced, pick what you want detail wise. Do the same with Volume and Animated Backrounds.
Close it and wahoo! Full Screen for Free Users!