--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -14020,24 +14020,25 @@ CSSParserImpl::ParseCounterData(nsCSSPro
       return false;
     }
 
     nsCSSValuePairList *cur = value.SetPairListValue();
     for (;;) {
       if (!ParseCustomIdent(cur->mXValue, mToken.mIdent, kCounterDataKTable)) {
         return false;
       }
-      if (!GetToken(true)) {
-        break;
-      }
-      if (mToken.mType == eCSSToken_Number && mToken.mIntegerValid) {
-        cur->mYValue.SetIntValue(mToken.mInteger, eCSSUnit_Integer);
-      } else {
-        UngetToken();
-      }
+      int32_t value = aPropID == eCSSProperty_counter_increment ? 1 : 0;
+      if (GetToken(true)) {
+        if (mToken.mType == eCSSToken_Number && mToken.mIntegerValid) {
+          value = mToken.mInteger;
+        } else {
+          UngetToken();
+        }
+      }
+      cur->mYValue.SetIntValue(value, eCSSUnit_Integer);
       if (!GetToken(true)) {
         break;
       }
       if (mToken.mType != eCSSToken_Ident) {
         UngetToken();
         break;
       }
       cur->mNext = new nsCSSValuePairList;

--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -8967,24 +8967,19 @@ nsRuleNode::ComputeContentData(void* aSt
       counterIncrementValue->GetPairListValue();
     MOZ_ASSERT(ourIncrement->mXValue.GetUnit() == eCSSUnit_Ident,
                "unexpected value unit");
     count = ListLength(ourIncrement);
     content->AllocateCounterIncrements(count);
 
     count = 0;
     for (const nsCSSValuePairList* p = ourIncrement; p; p = p->mNext, count++) {
-      int32_t increment;
-      if (p->mYValue.GetUnit() == eCSSUnit_Integer) {
-        increment = p->mYValue.GetIntValue();
-      } else {
-        increment = 1;
-      }
+      MOZ_ASSERT(p->mYValue.GetUnit() == eCSSUnit_Integer);
       p->mXValue.GetStringValue(buffer);
-      content->SetCounterIncrementAt(count, buffer, increment);
+      content->SetCounterIncrementAt(count, buffer, p->mYValue.GetIntValue());
     }
     break;
   }
 
   default:
     MOZ_ASSERT(false, "unexpected value unit");
   }
 
@@ -9015,24 +9010,19 @@ nsRuleNode::ComputeContentData(void* aSt
     const nsCSSValuePairList* ourReset =
       counterResetValue->GetPairListValue();
     MOZ_ASSERT(ourReset->mXValue.GetUnit() == eCSSUnit_Ident,
                "unexpected value unit");
     count = ListLength(ourReset);
     content->AllocateCounterResets(count);
     count = 0;
     for (const nsCSSValuePairList* p = ourReset; p; p = p->mNext, count++) {
-      int32_t reset;
-      if (p->mYValue.GetUnit() == eCSSUnit_Integer) {
-        reset = p->mYValue.GetIntValue();
-      } else {
-        reset = 0;
-      }
+      MOZ_ASSERT(p->mYValue.GetUnit() == eCSSUnit_Integer);
       p->mXValue.GetStringValue(buffer);
-      content->SetCounterResetAt(count, buffer, reset);
+      content->SetCounterResetAt(count, buffer, p->mYValue.GetIntValue());
     }
     break;
   }
 
   default:
     MOZ_ASSERT(false, "unexpected value unit");
   }
 

--- a/layout/style/test/mochitest.ini
+++ b/layout/style/test/mochitest.ini
@@ -140,18 +140,18 @@ support-files = file_bug645998-1.css fil
 [test_bug732209.html]
 support-files = bug732209-css.sjs
 [test_bug765590.html]
 [test_bug771043.html]
 [test_bug795520.html]
 [test_bug798567.html]
 [test_bug798843_pref.html]
 [test_bug829816.html]
+support-files = file_bug829816.css
 [test_bug874919.html]
-support-files = file_bug829816.css
 [test_bug887741_at-rules_in_declaration_lists.html]
 [test_bug892929.html]
 [test_bug1055933.html]
 support-files = file_bug1055933_circle-xxl.png
 [test_bug1089417.html]
 support-files = file_bug1089417_iframe.html
 [test_bug1112014.html]
 [test_bug1203766.html]

--- a/layout/style/test/stylo-failures.md
+++ b/layout/style/test/stylo-failures.md
@@ -49,17 +49,16 @@ to mochitest command.
   * test_bug413958.html `monitorConsole` [3]
   * test_parser_diagnostics_unprintables.html [550]
 * Transition support:
   * test_transitions.html: pseudo elements [4]
   * test_transitions_and_reframes.html `pseudo-element`: bug 1366422 [4]
   * Events:
     * test_animations_event_order.html [2]
 * test_computed_style.html `gradient`: -webkit-prefixed gradient values [13]
-* test_bug829816.html: counter-{reset,increment} serialization difference bug 1363968 [8]
 * dynamic change on \@counter-style rule bug 1363590
   * test_counter_style.html asserts [11]
   * test_counter_descriptor_storage.html asserts [110]
 * symbols() function and string value on list-style-type bug 1363596
   * test_value_storage.html `symbols(` [30]
   * ... `list-style-type` [8]
   * ... `'list-style'` [18]
 * Unimplemented \@font-face descriptors:

--- a/layout/style/test/test_bug829816.html
+++ b/layout/style/test/test_bug829816.html
@@ -24,27 +24,27 @@ https://bugzilla.mozilla.org/show_bug.cg
   <script type="application/javascript">
 
   /** Test for Bug 829816 **/
   var ss = document.styleSheets[1];
 
   for (var i = 0; i < 6; i++) {
     is(ss.cssRules[i].style.content, "\"\uFFFD\"",
         "\\0 in strings should be converted to U+FFFD");
-    is(ss.cssRules[i].style.counterReset, "\uFFFD",
+    is(ss.cssRules[i].style.counterReset, "\uFFFD 0",
         "\\0 in identifiers should be converted to U+FFFD");
   }
 
   is(document.styleSheets[2].cssRules[0].style.content, "\"\uFFFD\"",
       "U+0000 in strings should be converted to U+FFFD");
-  is(document.styleSheets[2].cssRules[0].style.counterReset, "\uFFFD",
+  is(document.styleSheets[2].cssRules[0].style.counterReset, "\uFFFD 0",
       "U+0000 in identifiers should be converted to U+FFFD");
   is(document.styleSheets[2].cssRules[1].style.content, "\"\uFFFD\"",
       "U+0000 in strings should be converted to U+FFFD");
-  is(document.styleSheets[2].cssRules[1].style.counterReset, "\uFFFD",
+  is(document.styleSheets[2].cssRules[1].style.counterReset, "\uFFFD 0",
       "U+0000 in identifiers should be converted to U+FFFD");
 
 
   </script>
 </head>
 <body>
 <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=829816">Mozilla Bug 829816</a>
 <p id="display"></p>