Since early February, Firefox users may have tripped on a Google AdSense security error. The error reads:
Security Error: Content at http://googleads.g.doubleclick.net/ may not load data from example.com
It happens on some configurations of Firefox, where the security prompt seems to be warning you that content from a third party is loading on this web page.
I honestly don't think this is a Google specific issue. It seems to be a setting that warns surfers of third party content showing up on a web page.
HowToGeek.com has an article that describes how you can "fix" this security prompt from showing. But in the AdSense case, it might not work.