CDN from code.jquery.com vs ajax.googleapis.com

CDN from code.jquery.com vs ajax.googleapis.com

Recently I had a web app stop working because of a problem loading the jquery mobile (and jquery) libraries from code.jquery.com but only in chrome and firefox (but not safari which loaded fine)...  I switched to ajax.googleapis.com and everything is back to being AOK.   I clearly don't quite understand what is going on.... can someone enlighten me?

Sorry if this is the wrong forum...