Disable scale image in Firefox
Follow @ggarron
By default Firefox scales images that are bigger than your screen or in fact bigger than the size of Firefox window at the time it is showing the image.
If you want to change this default behavior do it this way.
In the address bar enter this:
about:config
Then browse below until you see:
browser.enable_automatic_image_resizing
double click on it to change the boolean value from true to false, and you are done!.