Is it possible to find fire outside the Earth?
Many non-organic substances burn. For example:


Reactive metals such as potassium burn when exposed to oxygen. (Thanks to @Jon Custer in his comment)
Non metal elements such as carbon, sulphur and phosphorous also burn in oxygen when heated.


So yes fire is definitely possible outside earth.

Additionally simple organic compounds such as methane are known to exist in large quantities on other bodies such as Titan, a moon of Saturn, which has a whole 'hydrological' cycle based around methane, and to a lesser extent ethane and heavier hydrocarbons, with a methane atmosphere and lakes of methane on the surface. (Thanks to @ron in his comment)