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

.tabbrowser-tab[label*="Add-ons Manager"],
.tabbrowser-tab[label*="Add-ons Manager"][selected="true"]
{ -moz-appearance: none !important;
background: none !important;
border: transparent !important; 
box-shadow: inset 2px 0px 14px 0px rgba(254,0,0, .5) !important; 
color: #000 !important; }