I frequently go to Firefox to access pages with which Safari is unable to deal...and that includes Apple's own website where I was unable to buy a computer a while back.
Getting to the point, though, the problem may actually be on your end, but only in the sense that you're running browsers with which Comcast is only more or less compatible.
Much as we'd love it to be, Safari just plain isn't a dominant browser that commands the attention of every website builder...Apple apparently included.
But that doesn't excuse Comcast! (Dunno how you convince them of that, though.)
