This can be caused by a corrupt file, for the solution see Changes to toolbars and window sizes are not saved.

Nice try but that didn't solve the problem. My problem is specific to certain sites. A corrupt file would affect all sites the same. In any event, I tried your suggestion and it failed.

Check:

• http://kb.mozillazine.org/Websites_look_wrong
• http://kb.mozillazine.org/Website_colors_are_wrong

Can you attach a screenshot?

Use a compressed image type like PNG or JPG to save the screenshot and make sure that you do not exceed the maximum file size (1 MB) and do not click Preview after you have attached the image.
Make sure that you choose an unique name for the image to avoid problems with an already existing image.

If your attached image doesn't show then use an external hosting service like <ImageShack® - Hosting> and post a link to that image.

Let me just clarify this because apparently I was not specific enough. On the Firefox Toolbar, where icons can be placed, the sites I put there look fine until the next time I open Firefox, then some (not all) appear only as white squares, as they would look before Firefox gets the ico image. It's always the same sites and the others are always fine. Imagine a bunch of icons with a few white squares where icons should be between them. To put it another way, If 1 =an icon, and 0 = a white square, my toolbar looks like this:

11111110000101

I hope this makes it understandable.