diff --git a/dom/canvas/CanvasRenderingContextHelper.cpp b/dom/canvas/CanvasRenderingContextHelper.cpp
index 7c48103501d2..94c48616ba09 100644
--- a/dom/canvas/CanvasRenderingContextHelper.cpp
+++ b/dom/canvas/CanvasRenderingContextHelper.cpp
@@ -261,8 +261,9 @@ nsresult CanvasRenderingContextHelper::UpdateContext(
 nsresult CanvasRenderingContextHelper::ParseParams(
     JSContext* aCx, const nsAString& aType, const JS::Value& aEncoderOptions,
     nsAString& outParams, bool* const outUsingCustomParseOptions) {
-  // Quality parameter is only valid for the image/jpeg MIME type
-  if (aType.EqualsLiteral("image/jpeg")) {
+  // Quality parameter is only valid for the image/jpeg and image/webp MIME
+  // types.
+  if (aType.EqualsLiteral("image/jpeg") || aType.EqualsLiteral("image/webp")) {
     if (aEncoderOptions.isNumber()) {
       double quality = aEncoderOptions.toNumber();
       // Quality must be between 0.0 and 1.0, inclusive
diff --git a/dom/canvas/test/test_toDataURL_parameters.html b/dom/canvas/test/test_toDataURL_parameters.html
index 2cc8b0bb7f2c..b288e4d329ea 100644
--- a/dom/canvas/test/test_toDataURL_parameters.html
+++ b/dom/canvas/test/test_toDataURL_parameters.html
@@ -4,13 +4,13 @@
 <link rel="stylesheet" href="/tests/SimpleTest/test.css">
 <body>
 <p>
-This test covers the JPEG quality parameter. If (when) the HTML5 spec changes the
+This test covers the JPEG and webp quality parameter. If (when) the HTML5 spec changes the
 allowed parameters for ToDataURL, new tests should go here.
 </p>
 <canvas id="c" width="100" height="100"><p class="fallback">FAIL (fallback content)</p></canvas>
 <script>
-var canvas = document.getElementById('c');
-var ctx = canvas.getContext("2d");
+let canvas = document.getElementById('c');
+let ctx = canvas.getContext("2d");
 
 ctx.strokeStyle = '#FF0000';
 ctx.fillStyle = '#00FF00';
@@ -20,35 +20,44 @@ ctx.moveTo(10, 10);
 ctx.lineTo(90, 90);
 ctx.stroke();
 
-var pngData = canvas.toDataURL('image/png');
-var pngQuality = canvas.toDataURL('image/png', 0.1);
+let pngData = canvas.toDataURL('image/png');
+let pngQuality = canvas.toDataURL('image/png', 0.1);
 is(pngQuality, pngData, "Quality is not supported for PNG images");
 
-var data = canvas.toDataURL('image/jpeg');
-if (data.match(/^data:image\/jpeg[;,]/)) {
-    // Test the JPEG quality parameter
-    
-    var fullQuality = canvas.toDataURL('image/jpeg', 1.0);
-    var lowQuality = canvas.toDataURL('image/jpeg', 0.1);
-    isnot(lowQuality, fullQuality, "A low quality (0.1) should differ from high quality (1.0)");
-    
-    var medQuality = canvas.toDataURL('image/jpeg', 0.5);
-    isnot(medQuality, fullQuality, "A medium quality (0.5) should differ from high (1.0)");
-    isnot(medQuality, lowQuality, "A medium quality (0.5) should differ from low (0.5)");
-    
-    var tooHigh = canvas.toDataURL('image/jpeg', 2.0);
-    is(tooHigh, data, "Quality above 1.0 is treated as unspecified");
-    
-    var tooLow = canvas.toDataURL('image/jpeg', -1.0);
-    is(tooLow, data, "Quality below 0.0 is treated as unspecified");
-    
-    var lowQualityExtra = canvas.toDataURL('image/jpeg', 0.1, 'foo', 'bar', null);
-    is(lowQualityExtra, lowQuality, "Quality applies even if extra arguments are present");
-    
-    var lowQualityUppercase = canvas.toDataURL('IMAGE/JPEG', 0.1);
-    is(lowQualityUppercase, lowQuality, "Quality applies to image/jpeg regardless of case");
-    
-    var lowQualityString = canvas.toDataURL('image/jpeg', '0.1');
-    isnot(lowQualityString, lowQuality, "Quality must be a number (should not be a string)");
+function checkType(imagetype) {
+    let imageTypeString = 'image/' + imagetype;
+    let imageTypeUpperString = 'IMAGE/' + imagetype.toUpperCase();
+    let data = canvas.toDataURL(imageTypeString);
+    if (data.match(new RegExp('^data:image\/' + imagetype + '[;,]'))) {
+        // Test the JPEG/wepb quality parameter
+
+        let fullQuality = canvas.toDataURL(imageTypeString, 1.0);
+        let lowQuality = canvas.toDataURL(imageTypeString, 0.1);
+        isnot(lowQuality, fullQuality, "A low quality (0.1) should differ from high quality (1.0) " + imageTypeString);
+
+        let medQuality = canvas.toDataURL(imageTypeString, 0.5);
+        isnot(medQuality, fullQuality, "A medium quality (0.5) should differ from high (1.0) " + imageTypeString);
+        isnot(medQuality, lowQuality, "A medium quality (0.5) should differ from low (0.5) " + imageTypeString);
+
+        let tooHigh = canvas.toDataURL(imageTypeString, 2.0);
+        is(tooHigh, data, "Quality above 1.0 is treated as unspecified " + imageTypeString);
+
+        let tooLow = canvas.toDataURL(imageTypeString, -1.0);
+        is(tooLow, data, "Quality below 0.0 is treated as unspecified " + imageTypeString);
+
+        let lowQualityExtra = canvas.toDataURL(imageTypeString, 0.1, 'foo', 'bar', null);
+        is(lowQualityExtra, lowQuality, "Quality applies even if extra arguments are present " + imageTypeString);
+
+        let lowQualityUppercase = canvas.toDataURL(imageTypeUpperString, 0.1);
+        is(lowQualityUppercase, lowQuality, "Quality applies to " + imageTypeString + " regardless of case");
+
+        let lowQualityString = canvas.toDataURL(imageTypeString, '0.1');
+        isnot(lowQualityString, lowQuality, "Quality must be a number (should not be a string) " + imageTypeString);
+    } else {
+        ok(false, "should get a data url " + imageTypeString);
+    }
 }
+
+checkType('jpeg');
+checkType('webp');
 </script>
diff --git a/image/imgIEncoder.idl b/image/imgIEncoder.idl
index 11bdf4af6fe4..0e38a08bebbc 100644
--- a/image/imgIEncoder.idl
+++ b/image/imgIEncoder.idl
@@ -64,6 +64,13 @@ interface imgIEncoder : nsIAsyncInputStream
   // quality=#  --  default: "92"
   //    Quality of compression, 0-100 (worst-best).
   //    Quality >= 90 prevents down-sampling of the color channels.
+  //
+  //
+  // WEBP:
+  // -----
+  //
+  // quality=#  --  default: "92"
+  //    Quality of compression, 0-100 (worst-best).
 
 
   // Possible values for input format (note that not all image formats
