There is nothing *WRONG* with using mason jars to bottle your mead, just not commonly done. People store jams and jellies in mason jars all the time. In order to seal the jar and to ensure that all the beasties inside the fruit mixture are 100% dead, the mason jars are generally bathed in a nice hot bath. It is not necessary to cook the contents, as that could very well change the flavor of what you spent a long time making. All you need do is get the temperature high enough to kill off the yeasts and other bacterias.
If you are storing a sweeter mead in mason jars, be sure that all the yeasts are dead. If you are wrong, you could end up with bottle-bombs
. Should you be trying to avoid using chemicals, there are several ways of killing off the yeast. You can cold stabalize the mead, wait for all the yeast to drop to the bottom, then re-rack; wait a week to ensure that all the yeast are gone. Or you can let the yeast run it's course, re-rack when it is clear, and back-sweeten to taste. Or you can heat up the mason jar with the mead in it. The quickest way is to rack onto Sorbates and Sulfites...which is a whole 'nother discussion about the evils of chemicals
Anyway you do it, just make sure you enjoy the end product!