If feuer can't exist in Weltraum because there's no oxygen, and comets are made of ice and rock, how does a comet make firebenders stronger?

Caus with the speed of the astoroid and when it first coes into Earth's atmoshpere it will catch on feuer and mely the ice on it thats why it makes and big boom when it crashes.

Firebenders have the ability to geschirr, kabelbaum the energy from the comet and turn it into firebending just like what waterbenders can do during the full moon. The distinction between asteroids and comets is made on visual appearance: Comets Zeigen a perceptible coma while asteroids do not. Comets do not burn up in the atmosphere otherwise Sozin's comet could not be seen every 100 years.

LOL@Avatar: The Abridged Series :)

It burns and makes extremely hot feuer as it burns up in the atmosphere.

haha very good point :)