How are you testing?
#1 editor's built-in html preview
#2 opening .html files locally in various browsers
#3 pseudo-server such as WAMP
#4 in un-indexed directory of live server
The further removed you are from a real server, the more things won't work. So you need to know if things don't work because they can't work, or don't work because there is something wrong with them.
Just because you can do something in html doesn't mean you should do it. Know your audience. Nobody is going to rush out and get a new browser-- and the new OS to go with it-- just to be able to view one site as its designer intended.