Be advised that the video contains some strong language

Start off with jumping over the Goomba and snagging the mushroom. Run all the way to the ? block that you will obtain the fire flower from. When you activate the ? block time your jump perfectly so that Mario also hits the brick block right of the ? block. This will help dodge the 2nd Goomba that falls off the ledge above saving a few frames. Run left and enter the pipe. Jump and run right as soon as you hit the ground and then jump at the perfect time to not run over the exit pipe or lose time. Once you exit run right and perform a precise stair jump where you keep moving forward. You don't have that many frames to work with but you may have enough to swiftly swipe left on on the C-Pad or hold neutral to time the stair jump.

I've only gotten a 283 Fire Mario 4 times in my many attempts If you get it DON'T MESS UP YOUR SECOND RUN!!! imagine loosing the run because you failed to get 11s. I've done it twice. Don't be like me