Codeigniter / Firefox issue with “Document Expired” - works fine in other browsers

[eluser]kdawson[/eluser]
I do also see this message once in a while in Safari while having the developers inspector open.

"Resource interpreted as Image but transferred with MIME type text/html. admin_page:-1"

and then the source looks something like this :
"PCFkb2N0eXBlIGh0bWw+DQo8aHRtbD4NCjxoZWFkPg0KCQ0KCTxtZXRhIGh0dHAtZXF1aXY9IkNvbnRlbnQtVHlwZSIgY29udGVudD0idGV4dC9odG1sOyBjaGFyc2V0PX"

Not sure where my error is here. Or if one has anything to do with the other?

Thanks.