Bring to a boil. Lower temperature and maintain at a low boil for 2-3 hours, stirring occasionally to prevent sticking on the bottom. You want the salsa to reduce by about half as the tomato water boils off.
Wash jars and lids in hot soapy water and rinse. I use glass pint jars and metal lids and bands, but the original recipe writer says she used 3-cup plastic freezer containers. Just keep in mind that you want usable container sizes - so don't pour your salsa into gallon ziploc bags unless you plan on defrosting and eating a gallon of salsa at a time.
Fill jars with salsa, leaving about 1/2 inch to 3/4 inch space at the top for expansion during freezing. Let jars completely cool before putting on lids - this way you avoid condensation and ice on top of your salsa. Keep in freezer and thaw before eating.
I get a little smile when I open up our freezer and see an entire shelf of salsa. And, I confess that I will probably end up hiding half the jars from the Mr. because he loves this salsa so much, he'd eat a jar a day. So, some of the jars are visible. The rest are nicely tucked away under potato soup, blueberries, and frozen corn, to be pulled out in mid-February when I need a little boost ...