When I play it, even if I hold down space constantly on the first level, the rocket doesn't generate enough thrust to get off the ground. Does that in either Chrome or Firefox on Windows FWIW, but I get the feeling that's probably unrelated to the underlying issue. Assuming the game was working fine for you when you were developing it, the only think I can think of is if it's an issue of different framerates when you're in Unity vs in the WebGL build that're screwing up the physics if it's not scaling by Time.deltaTime (or if the scaling math didn't end up behaving like you would want it to). I hope you get it working 'cuz it looks like it might be an allright game if I could actually play it.