In order to save ammo, good fire bug only tap their mouse. So everything is burning, not dead. Even crawlers will burn for a few seconds on suicidal and HoE. So the problem comes to gorefasts. It actually take quite some ammo to take down. And he WILL BE ABLE to hit you even you keep backing off after lighted him. So you NEED to flame him down. And 6-man gorefasts will not die from just one burn. Light him again or flame him to death is the way.
Ok, so now we have some burning gorefasts getting close. And what a support do? A good support knows where to shoot to kill a line of FULL-HEALTH gorefasts. So, all those ammo used on all of the gorefasts is wasted. Bloats? You wait till he get close to see if that bloat explode first or youget puke on first? Any one will put a bullet in his head and gun him down, or, just hunting shotgun his from medium range TOGETHER with a bunch of gorefasts/clots/crawlers/stalker. Also, if you decap a bloat, he just drops. If you burn a bloat to death, he explode.
So, you should not be wasting ammo on ANY gorefasts, bloats, and most clearly, not husks too. And basically you dont do enough to kill scrakes and feshpounds. So, all you can shoot is clots, stalkers, crawlers and sirens.
That's why I agree firebug is outclassed by other perks.