Add this to line 10 in "nicetry.lua" and you'll also become immune to fire damage caused by molotovs. No more problems with trollers setting the escape van on fire or lighting up the no mercy elevator.
Doesn't seems to affect enviromental damage, I played goat simulator and I still got burnt by the building on fire.
The only con I found is that you won't get hurt by your own molotovs, so yakuza stealth players that uses the speed bonus from low health won't like to use it.

function PlayerDamage:damage_fire(attack_data, ...)
    local attacker_unit = attack_data and attack_data.attacker_unit
    if attacker_unit then
        if attacker_unit:movement():team() == self._unit:movement():team() then 
            --is fire aoe from friendly player
            return
        end
    end
end