After looking around the options, there IS an option to turn off music, and the sound. I guess you didn't look hard enough. No, they did NOT update it recently. The last one was in 2010. So don't try it.
MilhartRobert, there is a tab mute for a reason. Or if you're not using chrome, you can turn off sound from your desktop. If that's not helping, there's also a thing called headphones. Plug them in and don't use it. Done, no sound.
Also, you rated it a 1/5 just because you couldn't turn off the sound? Be more logical, maybe deduct a star from your original rating. Now if you rated it 2/5, I don't know why you would say "Nice game". So don't try it.
Tip for boss run: Upgrade your character stats to max, upgrade missile launcher to max, then complete the boss run. The missiles absorb shots coming towards you, and does a good amount of damage too.