Nothing to do with your slow connection. If both of Firefox and IE cannot viewing the images, the problem comes from wikipedia itself.
Wikipedia articles contributed by thousands of independent person, who helping wikipedia spread.
Maybe the contributor of the articles that you view not have basic html knowledge, maybe they break the code, without know what they do. Then, the picture cannot appears with well.
Mmm..friend, how about other articles in wikipedia. Do it showing the same behavior?