-khtml-opacity: .5; // old safari -moz-opacity: .5; // old firefox -ms-filter: alpha(opacity=50); // new ie -ms-filter: progid:DXImageTransform.Microsoft.Alpha(Opacity=50); // new ie filter: alpha(opacity=50); // old ie opacity: 0.5; // modern gecko and webkit
NOTE: Most old browsers are not used anymore, so this could be simplified to only:
filter: alpha(opacity=50); opacity: 0.5;