I don't mean to be nagging, but I would check that site some more in the validator if I were you. There are many errors, which make the site behave weird. It's 2016. Time to make websites that really work on *every* common platform
I know this can be frustrating, my sites aren't error-free either and I'm not saying that every 'warning' W3 throws at you should be taken too seriously. But it the layout of the site looks different in one of the major browsers, you really should fix it, I think.