Do NOT leave your freshies in a closed up vehicle (i.e., smashed between your sunshade, sun visor & the windshield) during the heat of summer in direct sunlight.  They can, and likely will, melt to some degree (like a plastic container put into the dishwasher when advised not to), but they will not melt like a wax candle, freshies are made from plastic aroma beads, not wax.

TAKE CAUTION when using in your car during temps +100˚ hot seasons & in direct summer sunlight, especially in southern states' heat - the melting point is 161°

In which states is it illegal to hang something from your rear view mirror?

According to WANE Arizona, California, Illinois, Minnesota, Pennsylvania, Texas, and Wisconsin.