Initially I thought this would be simple platformer, but the mechanic of leaving a trail of poison that becomes lethal means you can't just bounce around aimlessly, you have to think about your path through each level to ensure that you can complete it without bumping into the lethal poison.
Beyond the need for sound, I think that the way the poison trail (or the controls) works needs to be looked at. If you start moving and then stay still for too long, you end up being killed as the poison is still spawning where you're standing, and with the controls as they're set up now, it is very easy for a jump to fail or for you to fall off a ledge and into the poison trail. On one level I also got a stutter towards the end of the level which I assume is because of the number of poison spots that were spawned in and because I played through the browser. It might be possible to have a maximum number of these sprites that can spawn, and when that limit is reached you remove the oldest sprite. This would still leave a trail that could stop you from doubling back on yourself, but would help performance by limiting the number of poison sprites spawned at any given time.
Thanks for the game.
Any chance you could have a look at mine as well?