If you want to coat the glass rims with salt, spread some salt on a flat plate. Have ready 8 margarita glasses. Working with 1 glass at a time, dip the glass in water, dip the rim in the salt, and place the glass in the freezer to frost, about 30 minutes. If you are not using the salt, simply dip the glass in water and place in the freezer to frost.

Pass the oranges, lemon, and lime through a heavy-duty juicer, capturing the juice in a bowl or pitcher. Whisk the sugar into the juice until dissolved. Add the Cointreau, triple sec, and tequila and mix well. You should have about 2 cups.

In a blender, combine the citrus-tequila juice with 3 cups of the ice and process on high speed until a slushy consistency forms, about 1 minute. Add the remaining 3 cups ice and continue to process until smooth, about 2 minutes.

Divide evenly among the frosted glasses. Serve at once.