Pour the the margarita mix, tequila, Cointreau, Grand Marnier, and beer into the blender. For frozen margaritas, fill the blender with ice cubes and blend until the ice is crushed. (For margaritas on the rocks, use less ice and blend until the ingredients are thoroughly mixed.) The beer will create a frothy texture for the margarita. Dip the rim of the margarita glass in lime juice and then salt the rim with margarita salt.