Visit te showroom yesterday and noticed the firewall is filled with sound absorbing foam.

No. From the structure i guess there are 2 layers of firewall, inner layer towards dash and outer layer towards engine. There is a hollow space between this 2 layers, the foam is insert and filled this hollow space. Try to look at the 2nd pic, the foam is slit inside the space, not just paste at the firewall. I can confirm by try to poke and pull the foam by my finger. Same with the pic 1, the foam is extend from bottom to upper firewall and the upper foam is secured by wiper cover. So imagine it was a large piece of foam cover the whole firewall. Anyway, just my imagination.

However, just wonder what will happen if the foam absorb water? Since the foam is expose at the edge of wiper cover, during rain/car wash the water can enter that place and absorbed by foam, and by capillary action, at the end the whole foam will be soaked with water.