Fail to access JS functions in a signed script

In our web application we need to read/write several values from the registry, in order to achieve it we use the XPCOM interface in a script and signed it. (DRM.jar)

Our web app loads that Jar file in a hidden IFRAME ("DrmIFrame").
where its src="jar:DRM.jar!/DRM_FF_WIN.htm

And access/invoke its internal JS function in the following way
document.getElementById("DrmIFrame").contentWindow.GetClientID()

Its all works fine till the release of FireFox 3.0.

When trying to invoke the GetClientID function I had an exception which says: Permission denied to get property Window.GetClientID.

Then Ive tried asking for UniversalBrowserRead permission and yet got another exception:
document.getElementById("DrmIFrame").contentWindow. GetClientID is not a function.

My question is how I can access JS function in sign scripts in FireFox 3.0.Start Free Trial