"Firefox could not install the file at https://addons.mozilla.org/en-US/firefox/downloads/latest/1843/addon-1843-latest.xpi?src=external-getfirebug

     var itemLocation = e.location.getItemLocation(e.id).QueryInterface(Ci.nsILocalFile);

I'm trying to install the firebug addon in Firefox version 3.6.13 and get an error that reads: "Firefox could not install the file at https://addons.mozilla.org/en-US/firefox/downloads/latest/1843/addon-1843-latest.xpi?src=external-getfirebug because: Unexpected installation error Review the error console log for more details. -203" Error Log screen looks something like this: Error: e.location.getItemLocation(e.id) is null Source File: file:///C:/Program%20Files/Mozilla%20Firefox/components/nsExtensionManager.js Line: 3533 Code detail looks like this: var itemLocation = e.location.getItemLocation(e.id).QueryInterface(Ci.nsILocalFile); Anyone know how to resolve this?