The Yahoo Pingbox on my site appears in Chrome but not in Firefox (currently I've 3.6). Anyone have an idea why that might be?
That's because http://wgweb.msg.yahoo.com/badge/Pingbox.swf can only be downloaded if a Yahoo cookie is set, otherwise the server will respond with an error code. And I guess that you didn't visit any Yahoo web site with Firefox. Go to yahoo.com, then to your web page again - it will work. But don't ask me why Yahoo chose to implement it like this.