Plurk Without (troll) on Firefox

Since a few days ago, there are some troll emoticon introduced in plurk. There are some people just don’t like it and wanna delete it from their view. This is the CSS I wrote on Firefox to set no-display on it:

@namespace url(http://www.w3.org/1999/xhtml);
@-moz-document domain("plurk.com")  {
  img[alt='(troll)'], img[alt='(yay)'], img[alt='(fuu)'], img[alt='(bah)'], 
  img[alt='(gtroll)'], img[alt='(gyay)'], img[alt='(gfuu)'], img[alt='(gbah)'] {
    /* opacity:0.3; */ display:none;
  }
}