How do I fix this light fixture now unstuck from the ceiling?
1 - TURN OFF THE ELECTRICAL SUPPLY, preferably from the breaker, not just the switch.
Those two screws you see protruding from the box are there to hold up the light fixture. Extend these screws to their full length so that they are in the electrical box, but are as long as they can get.
Remove the glass and possibly the lightbulbs from the fixture.  You should see two slotted keyhole spaces that should line up with the screws.  Push the screws through the insulation and into the big parts of the holes. Rotate the fixture so the screws end up in the slots.
Tighten up the screws, but do not over-tighten.  Just tight enough to snug up the fixture to the ceiling.
Reinstall a light bulb, turn on the breaker and test the switch.  If it doesn't work, then remove and check to make sure the wires are all attached correctly. They might have jiggled loose during this process.
Reinstall the glass.
There is no adhesive. Don't use any adhesive.