Revealing mistake: Mrs. Doubtfire sets herself on fire. When she jumps back and starts fighting the flames, it is obviously a stunt double as her face is longer.
Suggested correction: If you look carefully, the face looks pretty much the same, as well as the voice.
The reason the voice was the same is that it was probably an audio dub, which is a voice recording over someone else's voice.
Revealing mistake: When the Hillards are at the pool, we see Stu, with his hairy chest, on the diving board. When the shot zooms out, we see a guy with no hair on his chest, who is obviously the stunt double.