Rinse the sticky rice several times until the water runs clear, then soak in water for at least 1 hour or overnight.
Steam or cook the rice using a rice cooker or steamer for 20–25 minutes until tender and sticky.
In a small pot, heat coconut milk, sugar, and salt over medium heat, stirring until sugar dissolves (do not boil).
Reserve ¼ cup of the coconut mixture and optionally thicken with cornstarch.
Mix the remaining coconut milk with the cooked sticky rice and let sit for 15 minutes to absorb.
Peel and dice the ripe mango into small cubes.
Layer popsicle molds with sticky rice at the bottom, followed by mango chunks, then a drizzle of reserved coconut sauce.
Repeat layers if needed until molds are full, then insert sticks.
Freeze for at least 6 hours or overnight until solid.
To release, run warm water over the outside of molds for a few seconds and gently pull out pops.