Testing Firewall now in epic quests. While not technically stacking like they did before, they stack.
Specifically, if you have several FWs and a mob is stationary, it seems to only take the standard 1 tic damage. However, throw a ton of FWs down, and any mob moving through them take damage each time they enter one, like entering a BB.
Charmed mobs continued to take damage in my FWs even when charmed. Charm and Mass Hold seemed to land well (need more testing). Occasionally an uncharmed mob would just stand around after charm broke.