Java around the world

I changed the java settings because i was getting these anoying security certificates and a friend said to turn java off..but they would still appear. I could not play videos on youtube and it would say : Hello, you either have JavaScript turned off or an old version of Adobe's Flash Player. Get the latest Flash player. But when i turn java back on i just get the same message and still cant play anything. help ! I have mozilla fire fox too..