I had that problem with the version of Firefox I was using. Updated it to a later version: Problem solved.
Before then, the way I solved it was I turned off Flash, moused over the menu, saved the URL from that menu item and stuck it in my bookmarks, then used the bookmark. (At some point later I'd remember to turn Flash back on... eventually.)
Since then the advert site that serves those must've been one of the ones really slowing things down and it got added to my Adblock Plus list, because I see those not at all anymore.
Near as I can tell, the owners of SN don't much care if the adverts adversely affect the functionality of the site. There has been a nearly constant stream of valid (IMO) complaints, for a couple years, now, about how they really mess things up, but the site's owners keep doing it, anyway. *shrug* It's their site and it's free to us, so can't really bitch.