Fastest Firemaking XP in OSRS

At level 90 firemaking, you can burn redwood logs, and these are faster than training at the wintertodt. With some focus, you can earn 510k firemaking xp per hour, whereas at the wintertodt you can only get a max of 330k per hour.

So redwoods are almost double the speed of the wintertodt, but getting from 90 to 99 will cost 9 mil. That’s not too expensive, but the wintertodt is profitable.