This is a complicated bug.
The fire resist potion still allows player to take fire damage from blazes.
If player takes enough damage from blaze's fireball that the armor breaks, it won't break. Instead it will error out This error will cause the game to crash every time you use 'E' Inventory. Opening a chest does not cause the game to crash. If player dies and drops the error-ed armor, game will crash if armor is picked up. Armor will disappear at that point.