You didn't capture the URL so we can all download it too?
Please can I ask a big favor of you?
If you could restore your phone (it will rollback to before the firmware update, but still have 8773) and download Wireshack
and monitor you internet connection in promiscuous mode. Enter filter: "http.request" (without the double quotes). Start to update your phone. You'll see all the webrequests it makes. You'll also see the cab file for the firmware update. It will look something like this: http://download.windowsupdate.com/ms...**********.cab
That's the address we all need to know in order to download the firmware update on our phones (like mine) which aren't receiving a notification on Zune.
EDIT: If you're not willing to do the above then please just tell us about your phone (what country, whether it is branded with a mobile phone company or unbranded, etc).