Chris,
are you trying to access data from different domain or with different protocol?
As long as your data is coming from same domain using same protocol, you should be able to use 'dbr.url' with external pages.
Ajax requests (which 'dbr.url' utilizes) have thing called same origin policy, which prevents document elements from accessing elements of a document from a different origin.
Note that popup elements are not supposed to include html, or head tags, just the data to be displayed.
See more information at:
http://en.wikipedia.org/wiki/Same_origin_policy
--
myDBR Team