Personal preference, but I've been used to using hot glue. When I install it, I'll "tack" it in with just small globs in various spots around the lid, that way, I can check it to make sure it's positioned properly and won't have to bust my butt removing should I need to adjust it. After I get it where it needs to be, I'll make larger globs where part is on the actual helmet and it merges onto the lip of the visor itself to "hold" onto it.
Thats just how I do it though.