I ran into the same problem. I solved it like this, the "moz-document url-prefix" is needed for FireFox. (The trick is ending with the SVG filter option).
.class {
filter: "progid:DXImageTransform.Microsoft.Dropshadow(OffX=12, OffY=12, Color='#444')";
-webkit-filter: drop-shadow(0px 0px 10px rgba(0,0,0,0.2));
filter: drop-shadow(0px 0px 10px rgba(0,0,0,0.2));
-ms-filter: url(#drop-shadow);
filter: url('#drop-shadow');
}
@-moz-document url-prefix() {
.class {
filter: drop-shadow(0px 0px 10px rgba(0,0,0,0.2));
}
}
You also need to include this in your HTML (or use an URL to reference an external SVG).
<svg height="0" width="0" xmlns="http://www.w3.org/2000/svg" style="position: absolute;">
<defs>
<filter id="drop-shadow">
<feGaussianBlur in="SourceAlpha" stdDeviation="10"/>
<feOffset dx="0" dy="0" result="offsetblur"/>
<feFlood flood-color="#000000" flood-opacity="0.2"/>
<feComposite in2="offsetblur" operator="in"/>
<feMerge>
<feMergeNode/>
<feMergeNode in="SourceGraphic"/>
</feMerge>
</filter>
</defs>
</svg>