There's a comment in dom/base/nsScriptLoader.cpp that says: // The nsScriptLoadRequest is passed as the context to necko, and thus // it needs to be threadsafe. Necko won't do anything with this // context, but it will AddRef and Release it on other threads. As far as I can see, this object is not used as a context since the changes in bug 1194526: the request object used be passed as the context parameter to nsIChannel::AsyncOpen(), but this was replaced with a call to AsyncOpen2() which doesn't take a context. Is is OK to get rid of this? The motivation for this is that it would be useful to make the request a cycle collected class for bug 1240072, so that it can contain a JS object pointer.