NoScript identified a URL for "updatemybrowser.org", but I enabled that and still did not get a pop-up.
So, it’s there. Maybe No-Script stopped you from seeing it.
If you look at the page source code, down at the very bottom, you’ll see the code for this script. Since the banner doesn’t appear on the Microsoft browser or on my WaterFox browser, it looks like the script is identifying my Seamonkey browser as being out of date, erroneously.