Firefox image messed up on some websites

On some websites (www.amtrak.com is an example), the dimensions of the displayed entities seem to be wrong or distorted. The result is that one part of the image overwrites another. In the case of Amtrak, it makes the Next button inaccessible because there's something else on top of it. I don't have this problem with the Windows version of Firefox. I'm sure that if the site builders had done things differently I wouldn't have this problem, but alas, I can't remake the world. Wherein lies the remedy? Paul