Running FF 51 (bit slow to update when it breaks add-ons) and IHG 1.6.5.5.1-signed.1-signed.
This is what I use to get imgbox working and to get around the click-through ad page they serve up before the image...it's only got to work until July...
Host Label:
imgbox
URL Pattern:
^http:\/\/(?:i\.)?imgbox\.com\/(?!(login|register|tos|help|dmca)).+
Search Pattern:
"REPLACE: 'http://imgbox.com/' , 'https://i.imgbox.com/'"