Paypal Button Isn't Working On Safari?

Hi, I am having a slight problem with my moms computer. I'm pretty sure the problem is with Safari & unfortunatly she won't let me download mozilla or chrome because she thinks it will somehow mess up her computer. For some reason Safari won't let me press the "buy" button to go to the check-out on this site "buy beats" & I know that it works because my friend Jimmy is the one who told me about the site & I watched him use the same paypal on his windows pc and it worked fine.

Any help and I will be very thankful