No.It appears my earlier questions went unnoticed, I'll repost them.
1. Is it possible to stack Flash fire? (if so how many?)
2. Is it possible to pass Flash fire?
3.Is Shedinja only vulnerable to SR due to his Rock Weakness?
No.
Not quite sure what you're asking.
Flash Fire
When this Pokémon is hit by a Fire move, it takes no damage, and all Fire moves used by this Pokémon are 50% stronger. Further hits by Fire moves simply do no damage, they do not boost damage further. This power boost is lost upon switching out. Will-O-Wisp also activates Flash Fire. If a Pokemon with Flash Fire is frozen, when it is hit by a Fire move, it will be defrosted and take damage without boosting Flash Fire.