wow ... ok thought the white part was broken.
ok heres what to do (or heres what i always do). get some windscreen grade black urethane, get your piece thats broken off and scuff that with a scotch brite abrasive pad. give the broken pieces and the bonding surface of the box itself a good key with the abrasive pad. then apply some urethane in and around the pieces and box, you can even build a mountain around it (be mindful of where and how the white piece needs to move, dont hinder it with urethane) put a piece of masking tape over it to hold it in place and wait 24 to 48 hours. urethane is better than any hard glues because it never goes hard, its flexible it will never crack off again.
for an even better hold clean all the surfaces with a paint thinner or wax and grease remover before applying the urethane.
ive done heaps of plastic stuff like this, works really well. both plastic bar sliders on my vp front bumper are adhered the same way. there never coming off.
franklinfrog's way would work too...