Put on a pair of rubber gloves and mix a mildew-killing cleaning solution consisting of 5 cups hot water and 1 cup chlorine bleach. Pour the solution into a clean spray bottle. If you would rather avoid using chlorine bleach, undiluted white vinegar will also work.
Spray the bleach solution or vinegar generously along the edges of the shower door molding. Leave the solution on the door for approximately five minutes, then use an old toothbrush to scrub along the molding and remove the mildew.
Rinse the solution off the shower door with clean water and wipe dry with a cloth or towel.