Change Channel Owner

gistfile1.js

    // Keep the URL the same so the browser sees it as the same.
    channel.originalURI = aRequest.URI;
    channel.asyncOpen(proxy, aContext);
    var securityManager = Cc["@mozilla.org/scriptsecuritymanager;1"].getService(Ci.nsIScriptSecurityManager);
    log('got secruity manager!');
    var uri = ioService.newURI('resource://pdf.js/web/viewer.html', null, null); 
    var principal = securityManager.getCodebasePrincipal(uri);
    log('created principal!');
    channel.owner = principal;
    log('hey we changed the owner!');

yury: did you try to remove the explicit principal swithcing but inherithing the loadGroup instead? Also, looking at the protocol handler for about:feed might be a good idea, too.