Posted by Ian Phillips on 31/01/2017 13:30:55:
But the advert is present on the Win 7 machine connected to the same router.
Ian P
Yes, but I think your Windows 7 machine is a new instance on the on the router and has its's own address cache.
I'm guessing the XP address cache in your router is partially corrupt, a theory you can easily disprove by resetting the router and not getting an improvement.
Right clicking on a page in Firefox opens up a menu with an 'Inspect Element' option. Clicking that will allow you to look at the web pages innards, which might reveal what's amiss.
Dave