Firefox question

Since updating to Firefox 3, I can't see things like the product images in Amazon "iframe" ads (I do see the rest of the ads though, and a blank space where the image would be), or the previews of Youtube clips on my flist (again just a big empty space, but I see them perfectly well when I open that particular post). It's the same at work and at home. Does anyone have an idea what could be the cause of this and how I can rectify that? I can't find anything in the Options that seems to fit. Thanks!!!