every video I have seen on firelands trash farming shows the person soloing the trash which looks like almost infinite amount of space to kite them. I zoned into a fresh firelands raid myself and the place is packed with mob packs. I mean the ramp you have to go down to get to the ground level has a molten behemoth walking up and down it. you can walk around him but I see no way to get all those mobs chasing you and have the room to kite them.

I think you need at least 1 boss down for the week, leave the instance and reset it. all the trash should respawn, and you just head to the area where the downed boss was killed and kite mobs around that area.