I clicked on All Collections, searched for an icon and found a few, but then I wanted to view other icons in it's collection. I don't see a way to do that, or even figure out that icon's source. Also, the "Search Icons" box is cleared when I move between collections. No (obvious?) way to sort the collections by the number of icons.
This feature's results page lists icons without mentioning from which collection they are, so therefore without providing the licensing information...