Firefox: When you click on a hyperlink image there is an active box that frames the image. If you happen to stay on the page after an image is clicked, the active box stays. Here’s one way to prevent this:

This has to be put into the css:

/* Remove focus rings (dotted rectangle) around active tabs */
tab:focus > .tab-middle { -moz-outline: none !important }

If that doesn’t fix the problem, add this into the css as well:
a
{
  outline: none;
}

 Hopefully, that will take care of the problem.