I've been making games with Java for quite a while now but when I got the idead of putting stuff up on the web I got a lot of problems. I tried the applet thing, but that's just old and doesn't really work on any browser anymore so I had to learn a new language. Now I've been remaking one of my first Java games in JavaScript/HTML5 and it works pretty well, at least for me.
Maybe you could try and see if you get any issues or something? What browser are you using in that case? MAC/PC?
Shoot with space, pause with P and steer with key arrows. When you have 50 in power the boss appears and you need to kill him before you reach earth.