Thanks to Jan Varga long ago, when you open and display a laaaaaarge image in Firefox (File > Open and pick up a large JPG for instance), it's resized and shrunk to fit, and you can click on it to go back to 1:1 scale.  But I was missing a very simple way to move the viewport over that 1:1 scale image without having to touch the two scrollbars. Basically, it was killing me to have that feature in my iPhone and have to deal with scrollbars in Firefox. So here's a trivial and a bit ugly patch to handle that behavior. Because I did not want to break drag-and-drop of an image, you have to press the mouse button AND the shift key when you want to move the viewport over the image. I have no idea if it's worth filing a RFE bug or even if it's a desireable feature for FF. I wanted it myself, period. (comments allowed on this post)

Click here to see the patch.