Apply Filter to Multiple Layers At Once (without converting to a SO)

The ideal way to do this would be to get some script that records your selected layers. There is some on this site, but you will have to search for it. It's a little involved - lengthy code. But basically, you would make a loop and loop through the layers and then apply the code you got from script listener. Something like this which will apply the filters to all top level layers, which is most likely what you don't want, but it will show you the structure:

var doc = activeDocument;
for(var i=0;i<doc.layers.length;i++){
     try{//the try will prevent the script from stopping if you try and apply the blur to layers that can't be blurred
          doc.activeLayer = doc.layers;

          gBlur()//putting your code in a separate function, keeps things neat and less cluttered.
     }
     catch(e){}
}

function gBlur(){
var idGsnB = charIDToTypeID( "GsnB" );
    var desc2 = new ActionDescriptor();
    var idRds = charIDToTypeID( "Rds " );
    var idPxl = charIDToTypeID( "#Pxl" );
    desc2.putUnitDouble( idRds, idPxl, 0.300000 );
executeAction( idGsnB, desc2, DialogModes.NO );
}//end function