Bug#640865: Images load automatically, even though image loading is disabled

[Kalle Olavi Niemitalo]

Possibly related upstream bugs:

Bug 331257 - data: images show up when 'load images' (Tools->Options->content->checkbox) is disabled
Bug 449273 - SVG:display desc (and title?) as text if images are blocked
Bug 1196784 - img tag with srcset attribute bypasses permissions.default.image=2

https://bugzilla.mozilla.org/buglist.cgi?bug_id=331257,449273,1196784