Firefox 4.0 support for printing embedded PDF files in iFrames via JavaScript

I recently upgraded to Firefox 4.0 and can no longer print embedded PDF documents contained in an iFrame. My company's web application has several pages which load PDF files from a Servlet into an iFrame. The pages in question all have "Print" buttons which when clicked executes a JavaScript function to obtain reference to the iframe containing the PDF, place it into focus() (e.g., frames['pdfdoc'].focus();), and invoke print() (e.g., frames['pdfdoc'].print();). There are no errors, or exceptions caught when the JavaScript function is invoked, but the "Print" button is no longer operational. Does Firefox 4.0 no longer support iFrames? The issue goes away if I revert back to ver 3.6.16