"Foaming a runway" may once have been done, I wouldn't know. It might even have achieved a purpose with aircraft full of gasoline, again, I wouldn't know. And I once ran an airport.
Nowadays it would be a good way to;
(a) reduce the AFS immediate capability to nearly zero (I suspect) shortly before a landing that is more likely to culminate in an emergency involving fire than most,
(b) close the runway for a long time while being cleaned
(c) create a huge environmental hazard with the foam constituents run-off, which could overwhelm the traps
(d) make it very difficult for emergency vehicles to approach a casualty
(e) flush large quantities of money down the toilet
while having no effect at all on the outcome of the event apart from the above.
I've always suspected that it's another media myth, but I'm sure someone can tell us the facts.