Interesting question. I guess both of these would translate as 'mousse' in French. First, the pronunciation: foam rhymes with 'home'. They are close in meaning, but I'd say that foam is thicker. For example: shaving foam. This is thick, so it's foam - not froth. Foam can even be almost solid, for example a mattress, or the padding in a sofa or cushion is called 'foam'. 'Froth' is thinner, and usually just on top or something, such as a beer or a cappuccino. I hope that answers your question.

In addition to what was said, the pronunciation is: foe - home (try this way) or for french, say: pronounce *l'eau* nce you get that *o* sound, put an *f* before it (f - eau) then add m = f - eau- m = foam (try it)