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Reliance on unsafeWindow means changes are now needed for compatibility with GM 2.0 and later. From the mozilla.org page:
"For stability, reliability, and security the privileged sandbox has been updated to match the new changes to unsafeWindow for the Add-on SDK. In order to write values to unsafeWindow you will need to use the new methods cloneInto(), exportFunction(), and/or createObjectIn()."