One thing that has not been mentioned (except as an
ingredient in oven cleaner): Potassium Hydroxide e.g.
liquid Draino.

Sodium, not potassium.

I use it all of the time to clean the smoke off glass
fireplace doors.

Yeah that works but is very toxic and would destroy any surface
besides glass.

It's not that toxic, and there are many plastics lye doesn't attack -- such
as ABS, which many bathtubs are made of. I spray Mr Muscle in the tub to get
rid of the soap scum. Works fine.

Mr Muscle was the winner in the "remove the smoke from the toaster oven
door" contest. I put a very small amount on a paper and rubbed firmly. You
can't do it in one sitting, as the lye starts to attack your fingers! But it
works.