Fire is an oxidizing chemical reaction, in the simplest sense it needs oxygen and fuel to burn in order to stay alight. But what reaction would you observe from a flammable substance like gasoline or lighter fluid in a vacuum?
If there's any trace of oxygen, and a spark, the vapors would burn like normal.
If there isn't any oxidising agent, it'll just vaporize and stay that way (maybe the vapors will attain equilibrium with the liquid if the vapor pressure is high enough, basically if there's enough liquid to start with).
That's mostly it... Nothing spectacular :)