There is no word "breakfirst". The only correct word for the morning meal is "breakfast".

This is an example of what is sometimes called an 'eggcorn'. It is a word that seems to make sense because it sounds like what we are trying to say. But it is mistaken. e.g. 'old timer's disease' instead of 'Alzheimer's disease' 'eggcorn' instead of 'acorn' http://en.wikipedia.org/wiki/Eggcorn