I don't want to prevent all images from loading or stop loading everything, I just want to stop loading an individual image after I've seen that it's probably not something I care about so I can use that bandwidth for something else.

My internet is very slow, but I still like browsing sites like tumblr, imgur, etc. that have lots of images. It seems like GIFs are getting more and more common and they can be several megabytes each... my internet just can't handle it.

When I right-click a broken/unloaded image in Firefox, there's an option to reload the image. I essentially want the counterpart to that: to right-click a still-loading image and stop the download. Is this possible? Greasemonkey script, extension, I'll take any method.