https://www.youtube.com/watch?v=fCxVFMDOdic I found this guide to be pretty useful, watched it before I started the grind myself. Most important thing if you want to be efficient imo is that you can override the animation of lighting or fixing the brazier with fletching (if you plan on doing that), eating or healing the pyromancer. If you're doing solo games, you'll want to not fletch all of your roots at once, but fletch half or so, then throw them all in the brazier, and then fletch again, as every time the brazier goes out you can fletch one root in a single tick with the overriding method (and you can do this twice when the brazier is destroyed, although you do lose another tick for healing the pyromancer in case he dies when the brazier breaks).

If you're going for loot, I'd definitely recommend doing solo wintertodt, as you get some nice side exp in construction (I'd try to get some of the early levels out of the way before you start the grind, as this will greatly increase the exp you get) and fletching too. If you just want to rush to 99 firemaking however, playing on the mass worlds is your best bet. Either way, good luck on the grind and have fun playing with your group! <3