If you're trying for the speedrun medal, do it on Chrome. Don't even bother on Firefox. Yes, it makes a huge difference!
Other than that, the rest of them are doable on Firefox.
I remember playing this a few years ago, and thinking it was just impossible. After grinding a while with the other 60 Second Run however... it's not too bad! Addicting; easy to replay, and once you figure out the pattern pretty rewarding too in how fast you can finish the levels. All that remains now is the speedrun, a whole other level of precision! Good game!
what is the secret medals