Can this be changed in Firefox?

I just downloaded Firefox to try out, but when I visit KirupaForum, There are ugly boxes round some things. (see attatchment.)

Do any of you other firefox users get this and is it possible to turn it off?

Up untill now I have been using the evil BT Yahoo Browser, which came free with my broadband. On this, the boxes have a much nicer, 3d look.