--- a/testing/web-platform/meta/web-animations/interfaces/Animatable/animate.html.ini
+++ b/testing/web-platform/meta/web-animations/interfaces/Animatable/animate.html.ini
@@ -1,9 +1,6 @@
 [animate.html]
   type: testharness
   [Element.animate() accepts a keyframe sequence with different composite values, but the same composite value for a given offset]
     expected: FAIL
     bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1291468
 
-  [Element.animate() accepts a single keyframe sequence with string offset]
-    expected: FAIL
-

--- a/testing/web-platform/meta/web-animations/interfaces/KeyframeEffect/constructor.html.ini
+++ b/testing/web-platform/meta/web-animations/interfaces/KeyframeEffect/constructor.html.ini
@@ -11,11 +11,8 @@
   [composite values are parsed correctly when passed to the KeyframeEffectReadOnly constructor in KeyframeTimingOptions]
     expected: FAIL
     bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1311620 # This needs additive animation
 
   [a KeyframeEffectReadOnly can be constructed with a keyframe sequence with different composite values, but the same composite value for a given offset]
     expected: FAIL
     bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1291468
 
-  [a KeyframeEffectReadOnly can be constructed with a single keyframe sequence with string offset]
-    expected: FAIL
-

--- a/testing/web-platform/meta/web-animations/interfaces/KeyframeEffect/setKeyframes.html.ini
+++ b/testing/web-platform/meta/web-animations/interfaces/KeyframeEffect/setKeyframes.html.ini
@@ -1,9 +1,6 @@
 [setKeyframes.html]
   type: testharness
   [Keyframes can be replaced with a keyframe sequence with different composite values, but the same composite value for a given offset]
     expected: FAIL
     bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1291468
 
-  [Keyframes can be replaced with a single keyframe sequence with string offset]
-    expected: FAIL
-

--- a/testing/web-platform/tests/web-animations/resources/keyframe-utils.js
+++ b/testing/web-platform/tests/web-animations/resources/keyframe-utils.js
@@ -254,17 +254,17 @@ var gKeyframeSequenceTests = [
              { offset: 1, computedOffset: 1, easing: "linear", left: "40px" }]
   },
   { desc:   "a single keyframe sequence with omitted offsets",
     input:  [{ left: "10px" }],
     output: [{ offset: null, computedOffset: 1, easing: "linear",
                left: "10px" }] },
   { desc:   "a single keyframe sequence with string offset",
     input:  [{ offset: '0.5', left: "10px" }],
-    output: [{ offset: 0.5, computedOffset: 1, easing: "linear",
+    output: [{ offset: 0.5, computedOffset: 0.5, easing: "linear",
                left: "10px" }] },
   { desc:   "a one property keyframe sequence with some omitted offsets",
     input:  [{ offset: 0.00, left: "10px" },
              { offset: 0.25, left: "20px" },
              { left: "30px" },
              { left: "40px" },
              { offset: 1.00, left: "50px" }],
     output: [{ offset: 0.00, computedOffset: 0.00, easing: "linear",