--- a/dom/canvas/test/webgl-conf/mochi-single.html
+++ b/dom/canvas/test/webgl-conf/mochi-single.html
@@ -48,16 +48,17 @@ if (parent) {
         parent.SimpleTest.requestLongerTimeout(timeoutLengthMultiplier);
       }
     }
   } catch (e) {
     console.log('Warning: No SpecialPowers.');
   }
 }
 
+SpecialPowers.pushPrefEnv({"set": [['webgl.force-enabled', true]]});
 ////////////////////////////////////////////////////////////////////////
 
 var testPath = location.search.substr(1);
 console.log('testPath: ' + testPath);
 frameElem.src = testPath;
 
 </script>
 </body>