Its actually quite easy to make fire snowballs. All you need is a snowy day, gloves, gas, and an empty scull.
First you make snowballs.
Second you pour gas on them
Third you light them
Fourth you throw them
One thing I found out is snow can be on fire without looking like it is. So keep the gas tank away from any snow. Or have a garden hose at the ready.
Remember don't try this at home. Leave it to the experts.