Comment 6 for bug 1442728

(any) & !(class=Totem) & !(class=MPlayer) & !(class=Vlc) & !(class=Plugin-container) & !(class=Firefox) & !(class=chromium-browser) & !(class=google-chrome)

Eleni, many of these values appear to be old or wrong. Here's what

$ xprop WM_CLASS | cut -d\" -f4
chromium-browser
$ xprop WM_CLASS | cut -d\" -f4
Totem
$ xprop WM_CLASS | cut -d\" -f4
vlc
$ xprop WM_CLASS | cut -d\" -f4
mplayer2
$ xprop WM_CLASS | cut -d\" -f4
Firefox
$ xprop WM_CLASS | cut -d\" -f4
google-chrome

I don't know were "plugin-container" comes from. mplayer2 is kind of new.

My suggestion:

(any) & !(class=Totem) & !(class=MPlayer) & !(class=mplayer2) & !(class=vlc) & !(class=Firefox) & !(class=chromium-browser) & !(class=google-chrome)

That fixes vlc, adds chromium-browser and google-chrome, leaves old MPlayer and adds new mplayer2. Firefox and Totem are unchanged.