Prepare the prickly pear fruit by removing the glochids. Slice down the prickly pear from the top to bottom and peel the skin off. Put the fruits in a pot and add enough water to cover.
Bring to a boil. Turn off the heat and allow to steep for 30 minutes.
Mash the fruit with a potato masher or, pour the contents of the pot in your high-powered blender. Blend until pureed.
Push through several layers of cheesecloth or a fine mesh strainer to remove the seeds.
Measure the strained juice - pour into an empty pot. Add an equal parts of sugar. Bring to a simmer over medium heat for 5 minutes.
Turn off the heat. Let it cool for 15 minutes. Add the citric acid (or lemon juice) - 1/4 tsp per pint, and 1/2 tsp for a quart. Add your lids and screw bands to the jars and tighten.
Process the jars in a water bath. Cover with an inch of water and boil for 15 minutes (pint) or 20 minutes (quart). Lift the jars out of the water with tongs and set them aside in a safe place to cool down.