A few patches ago it didn't work on "sticks and stones", the poor monkey's version of shuriken. I thought it was deliberate since they can throw two each round.
Would open some fun tactics if it was changed, but perhaps a bit strong even with horrible friendly fire issues.
It works on any weapons for which there is a fire version:
214 Fire Arbalest
425 Fire Boulder
215 Fire Boulder (Edi's database doesn't show a fire effect for this one.)
217 Fire Bow of War
406 Fire Chakram
356 Fire Composite Bow
213 Fire Crossbow
209 Fire Javelin
212 Fire Long Bow
211 Fire Short Bow
407 Fire Shuriken
210 Fire Sling
405 Fire Small Bow