You can do this:
1. Enable fullscreen mode: Go to your browser's “View” menu and find “Full Screen”. Or just press with the mouse on the browser's URL input field and press F11 key.
2. Use the mouse to scroll the Window: Hold “w” key down and move with the mouse up or down to scroll the window. You can also hold Ctrl key and move the mouse to the sides of the window.
3. When zoomed in, press “s” key and move with mouse to scroll the zoom area or move the zoom box on the page thumbnail in the Pages panel.
See shortcuts page for more shortcuts: http://www.fatpaint.com/shortcuts
Or just go to editor window menu and choose “Shortcut keys” under the menu Help.