The internal viewer should have options similiar to those of the standalone viewer. like pressing "o" to show the original size. In that mode, using the arrow keys should move around the image. Additionally, the maximum height should be used (as an option), even covering the status bar, & leaving out the upper control elements, which are only usable with the mouse. They all could be replaced by keyboard commands, left & right arrow keys to browse (unless in full screen mode, where it moves the image around).