Gave it another test and although the volumetric fog seems to work, it’s showing weird white outline artifacts on my machine (Macbook Pro, ATI x1600 graphics, OS X 10.6.8, tested with both Chrome and Firefox).
Those problems should be fixed in the next version I just submitted to the Asset Store. Unity 3.5 is now supported also. The demos should now work in webplayer 3.4 and 3.5.
Working on a game for a low-end device, does this require additional camera passes/render textures, or were you able to do it with some clever shader passes?