I am using 11.2 & Gnome
From what I have found NX depends on ESD.
If you enable multimedia on the nomachine client you will not be able to start firefox. Reference my post here Firefox is broken/will not start - openSUSE Forums
The only way you can start firefox is by using the command noted in this post LD_PRELOAD keeping mozilla from starting - openSUSE Forums
# LD_PRELOAD="" firefox
Xlib: extension "Generic Event Extension" missing on display ":1026.0".
Xlib: extension "Generic Event Extension" missing on display ":1026.0".
Xlib: extension "Generic Event Extension" missing on display ":1026.0".
Xlib: extension "Generic Event Extension" missing on display ":1026.0".
Xlib: extension "Generic Event Extension" missing on display ":1026.0".
*** nss-shared-helper: Shared database disabled (set NSS_USE_SHARED_DB to enable).
You than must leave this terminal window open otherwise you will close you firefox session. You still will have no sound through NX.
Here is what I have found on the nomachine web site NoMachine NX - Support: Article
Has anyone been able to get sound to play through the NX client? I am interested in only getting flash player to forward sound i.e. youtube.