@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

#searchbar .searchbar-box:not(focused), #searchbar .searchbar-textbox:not(focused) .search-go-button
{
  opacity: 0.5 !important; 
}

#searchbar .searchbar-box[focused="true"], #searchbar .searchbar-textbox[focused="true"] .search-go-button
{
  opacity: 1 !important; 
}