The problem is solved, except for one server www12
If you click on a thumbnail and the image is still being pushed-off the right edge of the browser, chances are that it says, at the bottom of your screen, Served by www12.imagefap.com.
Change the url to www10, www11, or www13.imagefap.com and the problem no longer exists. This solution is only temporary, tomorrow morning a sysadmin is available to delete some cached template files
Of course you still have to scroll if you open a full image that is larger than your screen resolution (on my screen larger than 1920x1080)