Possibly - yahooanything perhaps ...
I was beginning to wonder that. You can block certain domains in some routers, so check that. Also - I had a weird problem with a Netgear router once, although I'm not criticising Netgear specifically - they seem to have a good reputation. I guess mine was faulty. It would randomly suddenly start blocking some websites, or some parts of some websites for no particular reason. Nothing was set in the content filtering page, and a reboot of the router would fix it. Until a few days or weeks later when it would start playing up again.
Ok, just checked my router firwall settings and there was an option under the security settings to block pop-up menu's which was checked. I unchecked this option and now i have the puilldown menu's! this topic is solved!