YSlow always tells me my content is not served from a CDN

"Try restarting firefox after you change the setting.

For me, I specified the domain name as ""cdn.ourdomain.com"" - no http://. Then, when I ran yslow, it showed:

Using these CDN hostnames from your preferences: cdn.ourdomain.com

but it was ignoring the setting. Restarting firefox and rerunning yslow seemed to do the trick."