Deserialization is used in non JSDOMGlobalObject context for IDB in NetworkProcess to get access to the value in case of key path use. Currently, deserialization fails as DOM objects require a JDOMGlobalObject. In the context of IDB, there is no need for the exact JS wrapper. An empty object might be sufficient if the key path is not a property or sub property of the JS DOM object.
*** This bug has been marked as a duplicate of bug 192606 ***