You're misunderstanding this. The "Resize to Full Screen" text is a Bookmarklet; you click and drag it to your Bookmark Bar in Safari, then click on it from there to resize your screen. But apparently those don't work in the forums, so here's the raw code:
javascript:self.moveTo(0,0);self.resizeTo(screen.availWidth,screen.availHeight);
Create a new Bookmark (copy one if you need to just to get the necessary fields in Safari without creating a folder), copy/paste that code for the Location or URL field, then place it on your Bookmark Bar.
Mulder