It's not ideal, but if you know how to create your own custom stylesheet, or use the Stylish FF extension, you can fix it with this:
Code:
@namespace url(http://www.w3.org/1999/xhtml);
@-moz-document domain("www.photoradar.com") {
a.menu-1-2-106-active {
background: url(http://static.photoradar.com/sites/all/themes/photoradar/media/images/global-nav-bck-active.gif) no-repeat 50% -3px !important;
}
}