A note to users of the Firefox internet browser:

This browser does not always allow PayPal buttons to display or function properly.  To remedy this situation, clear the browser's cache and cookies (see below), then try again.  Alternatively, switch to the Internet Explorer browser which doesn't experience such issues.

How to clear the Firefox cache and cookies:
  1. While in Firefox, click on the Tools link at the top of the window. 
    Once it opens, click on Options.
    In the Options window, click on the Privacy tab at the top.
    In the Private Data box, click on Clear Now.
    In the new box that opens, ensure that there are checks beside Cache and Cookies. 
    Click on Clear Private Data Now.
    Now try the PayPal button again.  This time, everything should work as designed.