diff --git a/layout/reftests/webm-video/generate-object-position-video-tests.sh b/layout/reftests/webm-video/generate-object-position-video-tests.sh
new file mode 100644
index 000000000000..f6210248e880
--- /dev/null
+++ b/layout/reftests/webm-video/generate-object-position-video-tests.sh
@@ -0,0 +1,78 @@
+#!/bin/bash
+#
+# Any copyright is dedicated to the Public Domain.
+# http://creativecommons.org/publicdomain/zero/1.0/
+#
+# Script to generate <video src> reftest files, from corresponding reftest
+# files that use <video poster>.
+#
+# This script expects to be run from this working directory:
+#  mozilla-central/layout/reftests/w3c-css/submitted/images3
+#
+# It requires that the tools png2yuv and vpxenc be available, from the
+# Ubuntu packages 'mjpegtools' and 'vpx-tools'. More info here:
+#  http://wiki.webmproject.org/howtos/convert-png-frames-to-webm-video
+
+VIDEO_REFTEST_PATH="../../../webm-video"
+
+imageFileArr=("colors-16x8.png" "colors-8x16.png")
+numImageFiles=${#imageFileArr[@]}
+
+# Copy image files, and generate webm files:
+for ((i = 0; i < $numImageFiles; i++)); do
+  imageFileName=${imageFileArr[$i]}
+  imageDest=$VIDEO_REFTEST_PATH/$imageFileName
+
+  echo "Copying $imageDest."
+  hg cp support/$imageFileName $imageDest
+
+  videoDest=`echo $imageDest | sed "s/png/webm/"`
+  echo "Generating $videoDest."
+  png2yuv -f 1 -I p -b 1 -n 1 -j $imageDest \
+    | vpxenc --passes=1 --pass=1 --codec=vp9 --lossless=1 --max-q=0 -o $videoDest -
+  hg add $videoDest
+done
+
+reftestListFileName="$VIDEO_REFTEST_PATH/reftest.list"
+
+# Loop across all <video poster> tests:
+for origTestName in object-position-png-*p.html; do
+  # Find the corresponding reference case:
+  origReferenceName=$(echo $origTestName |
+                      sed "s/p.html/-ref.html/")
+
+  # The generated testcase will have "-webm" instead of "-png", and unlike
+  # the original png test, it won't have a single-letter suffix to indicate the
+  # particular container element. (since it's unnecessary -- there's only one
+  # possible container element for webm, "<video>")
+  videoTestName=$(echo $origTestName |
+                  sed "s/png/webm/" |
+                  sed "s/p.html/.html/")
+
+  videoReferenceName=$(echo $videoTestName |
+                       sed "s/.html/-ref.html/")
+
+  # Generate reference file (dropping "support" subdir from image paths):
+  echo "Copying $origReferenceName to $VIDEO_REFTEST_PATH."
+  videoReferenceFullPath=$VIDEO_REFTEST_PATH/$videoReferenceName
+  hg cp $origReferenceName $videoReferenceFullPath
+  sed -i "s,support/,," $videoReferenceFullPath
+
+  # Generate testcase
+  # (converting <video poster="support/foo.png"> to <video src="foo.webm">):
+  echo "Generating $videoTestName from $origTestName."
+  videoTestFullPath=$VIDEO_REFTEST_PATH/$videoTestName
+  hg cp $origTestName $videoTestFullPath
+  sed -i "s/PNG image/WebM video/" $videoTestFullPath
+  sed -i "s/poster/src/" $videoTestFullPath
+  sed -i "s,support/,," $videoTestFullPath
+  sed -i "s/png/webm/" $videoTestFullPath
+  sed -i "s/$origReferenceName/$videoReferenceName/" $videoTestFullPath
+
+  # Update reftest manifest:
+  annotation="fails-if(layersGPUAccelerated) skip-if(Android||B2G)"
+  comment="# Bug 1098417 for across-the-board failure, Bug 1083516 for layersGPUAccelerated failures, Bug 1084564 for Android/B2G failures"
+  echo "$annotation == $videoTestName $videoReferenceName $comment" \
+    >> $reftestListFileName
+
+done
diff --git a/layout/reftests/webm-video/object-position-webm-001-ref.html b/layout/reftests/webm-video/object-position-webm-001-ref.html
new file mode 100644
index 000000000000..4a1267a4fd23
--- /dev/null
+++ b/layout/reftests/webm-video/object-position-webm-001-ref.html
@@ -0,0 +1,42 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>CSS Reftest Reference</title>
+    <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+    <style type="text/css">
+      div {
+        background: lightgray;
+        margin-right: 2px;
+        background-image: url("colors-16x8.png");
+        background-size: contain;
+        background-repeat: no-repeat;
+        float: left;
+        width: 20px;
+        height: 20px;
+      }
+
+      .op_y-7  { background-position: 50%  -7% }
+      .op_y13  { background-position: 50%  13% }
+      .op_y23  { background-position: 50%  23% }
+      .op_y50  { background-position: 50%  50% }
+      .op_y75  { background-position: 50%  75% }
+      .op_y88  { background-position: 50%  88% }
+      .op_y111 { background-position: 50% 111% }
+
+    </style>
+  </head>
+  <body>
+    <div class="op_y-7"></div>
+    <div class="op_y13"></div>
+    <div class="op_y23"></div>
+    <div class="op_y50"></div>
+    <div class="op_y75"></div>
+    <div class="op_y88"></div>
+    <div class="op_y111"></div>
+  </body>
+</html>
diff --git a/layout/reftests/webm-video/object-position-webm-001.html b/layout/reftests/webm-video/object-position-webm-001.html
new file mode 100644
index 000000000000..90e7881e6101
--- /dev/null
+++ b/layout/reftests/webm-video/object-position-webm-001.html
@@ -0,0 +1,44 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>CSS Test: various 'object-position' values on a fixed-size video element, with a WebM video and 'object-fit:contain'.</title>
+    <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+    <link rel="help" href="http://www.w3.org/TR/css3-images/#sizing">
+    <link rel="help" href="http://www.w3.org/TR/css3-images/#the-object-fit">
+    <link rel="help" href="http://www.w3.org/TR/css3-images/#the-object-position">
+    <link rel="match" href="object-position-webm-001-ref.html">
+    <style type="text/css">
+      video {
+        background: lightgray;
+        margin-right: 2px;
+        object-fit: contain;
+        float: left;
+        width: 20px;
+        height: 20px;
+      }
+
+      .op_y-7  { object-position: 50%  -7% }
+      .op_y13  { object-position: 50%  13% }
+      .op_y23  { object-position: 50%  23% }
+      .op_y50  { object-position: 50%  50% }
+      .op_y75  { object-position: 50%  75% }
+      .op_y88  { object-position: 50%  88% }
+      .op_y111 { object-position: 50% 111% }
+
+    </style>
+  </head>
+  <body>
+    <video src="colors-16x8.webm" class="op_y-7"></video>
+    <video src="colors-16x8.webm" class="op_y13"></video>
+    <video src="colors-16x8.webm" class="op_y23"></video>
+    <video src="colors-16x8.webm" class="op_y50"></video>
+    <video src="colors-16x8.webm" class="op_y75"></video>
+    <video src="colors-16x8.webm" class="op_y88"></video>
+    <video src="colors-16x8.webm" class="op_y111"></video>
+  </body>
+</html>
diff --git a/layout/reftests/webm-video/object-position-webm-002-ref.html b/layout/reftests/webm-video/object-position-webm-002-ref.html
new file mode 100644
index 000000000000..8c687d3e9bf0
--- /dev/null
+++ b/layout/reftests/webm-video/object-position-webm-002-ref.html
@@ -0,0 +1,42 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>CSS Reftest Reference</title>
+    <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+    <style type="text/css">
+      div {
+        background: lightgray;
+        margin-right: 2px;
+        background-image: url("colors-8x16.png");
+        background-size: contain;
+        background-repeat: no-repeat;
+        float: left;
+        width: 20px;
+        height: 20px;
+      }
+
+      .op_x-7  { background-position:  -7% 50% }
+      .op_x13  { background-position:  13% 50% }
+      .op_x23  { background-position:  23% 50% }
+      .op_x50  { background-position:  50% 50% }
+      .op_x75  { background-position:  75% 50% }
+      .op_x88  { background-position:  88% 50% }
+      .op_x111 { background-position: 111% 50% }
+
+    </style>
+  </head>
+  <body>
+    <div class="op_x-7"></div>
+    <div class="op_x13"></div>
+    <div class="op_x23"></div>
+    <div class="op_x50"></div>
+    <div class="op_x75"></div>
+    <div class="op_x88"></div>
+    <div class="op_x111"></div>
+  </body>
+</html>
diff --git a/layout/reftests/webm-video/object-position-webm-002.html b/layout/reftests/webm-video/object-position-webm-002.html
new file mode 100644
index 000000000000..f2980189a4b4
--- /dev/null
+++ b/layout/reftests/webm-video/object-position-webm-002.html
@@ -0,0 +1,44 @@
+<!DOCTYPE html>
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>CSS Test: various 'object-position' values on a fixed-size video element, with a WebM video and 'object-fit:contain'.</title>
+    <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+    <link rel="help" href="http://www.w3.org/TR/css3-images/#sizing">
+    <link rel="help" href="http://www.w3.org/TR/css3-images/#the-object-fit">
+    <link rel="help" href="http://www.w3.org/TR/css3-images/#the-object-position">
+    <link rel="match" href="object-position-webm-002-ref.html">
+    <style type="text/css">
+      video {
+        background: lightgray;
+        margin-right: 2px;
+        object-fit: contain;
+        float: left;
+        width: 20px;
+        height: 20px;
+      }
+
+      .op_x-7  { object-position: -7%  50% }
+      .op_x13  { object-position: 13%  50% }
+      .op_x23  { object-position: 23%  50% }
+      .op_x50  { object-position: 50%  50% }
+      .op_x75  { object-position: 75%  50% }
+      .op_x88  { object-position: 88%  50% }
+      .op_x111 { object-position: 111% 50% }
+
+    </style>
+  </head>
+  <body>
+    <video src="colors-8x16.webm" class="op_x-7"></video>
+    <video src="colors-8x16.webm" class="op_x13"></video>
+    <video src="colors-8x16.webm" class="op_x23"></video>
+    <video src="colors-8x16.webm" class="op_x50"></video>
+    <video src="colors-8x16.webm" class="op_x75"></video>
+    <video src="colors-8x16.webm" class="op_x88"></video>
+    <video src="colors-8x16.webm" class="op_x111"></video>
+  </body>
+</html>
diff --git a/layout/reftests/webm-video/reftest.list b/layout/reftests/webm-video/reftest.list
index e194fd2e006d..b55f55d8536b 100644
--- a/layout/reftests/webm-video/reftest.list
+++ b/layout/reftests/webm-video/reftest.list
@@ -50,3 +50,5 @@ fails-if(layersGPUAccelerated) skip-if(Android||B2G) == object-fit-none-webm-001
 fails-if(layersGPUAccelerated) skip-if(Android||B2G) == object-fit-none-webm-002.html object-fit-none-webm-002-ref.html # Bug 1083516 for layersGPUAccelerated failures, Bug 1084564 for Android/B2G failures
 fails-if(layersGPUAccelerated) skip-if(Android||B2G) == object-fit-scale-down-webm-001.html object-fit-scale-down-webm-001-ref.html # Bug 1083516 for layersGPUAccelerated failures, Bug 1084564 for Android/B2G failures
 fails-if(layersGPUAccelerated) skip-if(Android||B2G) == object-fit-scale-down-webm-002.html object-fit-scale-down-webm-002-ref.html # Bug 1083516 for layersGPUAccelerated failures, Bug 1084564 for Android/B2G failures
+fails-if(layersGPUAccelerated) skip-if(Android||B2G) fails == object-position-webm-001.html object-position-webm-001-ref.html # Bug 1098417 for across-the-board failure, Bug 1083516 for layersGPUAccelerated failures, Bug 1084564 for Android/B2G failures
+fails-if(layersGPUAccelerated) skip-if(Android||B2G) fails == object-position-webm-002.html object-position-webm-002-ref.html # Bug 1098417 for across-the-board failure, Bug 1083516 for layersGPUAccelerated failures, Bug 1084564 for Android/B2G failures
