--- a/accessible/generic/Accessible-inl.h
+++ b/accessible/generic/Accessible-inl.h
@@ -66,28 +66,34 @@ inline bool Accessible::IsSearchbox() co
 }
 
 inline bool Accessible::HasGenericType(AccGenericType aType) const {
   const nsRoleMapEntry* roleMapEntry = ARIARoleMap();
   return (mGenericTypes & aType) ||
          (roleMapEntry && roleMapEntry->IsOfType(aType));
 }
 
-inline bool Accessible::HasNumericValue() const {
-  if (mStateFlags & eHasNumericValue) return true;
+inline bool Accessible::NativeHasNumericValue() const {
+  return mStateFlags & eHasNumericValue;
+}
 
+inline bool Accessible::ARIAHasNumericValue() const {
   const nsRoleMapEntry* roleMapEntry = ARIARoleMap();
   if (!roleMapEntry || roleMapEntry->valueRule == eNoValue) return false;
 
   if (roleMapEntry->valueRule == eHasValueMinMaxIfFocusable)
     return InteractiveState() & states::FOCUSABLE;
 
   return true;
 }
 
+inline bool Accessible::HasNumericValue() const {
+  return NativeHasNumericValue() || ARIAHasNumericValue();
+}
+
 inline bool Accessible::IsDefunct() const {
   MOZ_ASSERT(mStateFlags & eIsDefunct || IsApplication() || IsDoc() ||
                  mStateFlags & eSharedNode || mContent,
              "No content");
   return mStateFlags & eIsDefunct;
 }
 
 inline void Accessible::ScrollTo(uint32_t aHow) const {

--- a/accessible/generic/Accessible.cpp
+++ b/accessible/generic/Accessible.cpp
@@ -1372,18 +1372,22 @@ void Accessible::Value(nsString& aValue)
     // equivalent. For the string value, we will try the optional text
     // equivalent first.
     if (!mContent->IsElement()) {
       return;
     }
 
     if (!mContent->AsElement()->GetAttr(kNameSpaceID_None,
                                         nsGkAtoms::aria_valuetext, aValue)) {
-      mContent->AsElement()->GetAttr(kNameSpaceID_None,
-                                     nsGkAtoms::aria_valuenow, aValue);
+      if (!NativeHasNumericValue()) {
+        double checkValue = CurValue();
+        if (!IsNaN(checkValue)) {
+          aValue.AppendFloat(checkValue);
+        }
+      }
     }
     return;
   }
 
   if (!roleMapEntry) {
     return;
   }
 
@@ -1407,29 +1411,37 @@ void Accessible::Value(nsString& aValue)
       }
     }
 
     if (option) nsTextEquivUtils::GetTextEquivFromSubtree(option, aValue);
   }
 }
 
 double Accessible::MaxValue() const {
-  return AttrNumericValue(nsGkAtoms::aria_valuemax);
+  double checkValue = AttrNumericValue(nsGkAtoms::aria_valuemax);
+  return IsNaN(checkValue) && !NativeHasNumericValue() ? 100 : checkValue;
 }
 
 double Accessible::MinValue() const {
-  return AttrNumericValue(nsGkAtoms::aria_valuemin);
+  double checkValue = AttrNumericValue(nsGkAtoms::aria_valuemin);
+  return IsNaN(checkValue) && !NativeHasNumericValue() ? 0 : checkValue;
 }
 
 double Accessible::Step() const {
   return UnspecifiedNaN<double>();  // no mimimum increment (step) in ARIA.
 }
 
 double Accessible::CurValue() const {
-  return AttrNumericValue(nsGkAtoms::aria_valuenow);
+  double checkValue = AttrNumericValue(nsGkAtoms::aria_valuenow);
+  if (IsNaN(checkValue) && !NativeHasNumericValue()) {
+    double minValue = MinValue();
+    return minValue + ((MaxValue() - minValue) / 2);
+  }
+
+  return checkValue;
 }
 
 bool Accessible::SetCurValue(double aValue) {
   const nsRoleMapEntry* roleMapEntry = ARIARoleMap();
   if (!roleMapEntry || roleMapEntry->valueRule == eNoValue) return false;
 
   const uint32_t kValueCannotChange = states::READONLY | states::UNAVAILABLE;
   if (State() & kValueCannotChange) return false;

--- a/accessible/generic/Accessible.h
+++ b/accessible/generic/Accessible.h
@@ -896,16 +896,26 @@ class Accessible : public nsISupports {
   /**
    * Return true if the accessible has associated DOM content.
    */
   bool HasOwnContent() const {
     return mContent && !(mStateFlags & eSharedNode);
   }
 
   /**
+   * Return true if native markup has a numeric value.
+   */
+  bool NativeHasNumericValue() const;
+
+  /**
+   * Return true if ARIA specifies support for a numeric value.
+   */
+  bool ARIAHasNumericValue() const;
+
+  /**
    * Return true if the accessible has a numeric value.
    */
   bool HasNumericValue() const;
 
   /**
    * Return true if the accessible state change is processed by handling proper
    * DOM UI event, if otherwise then false. For example, CheckboxAccessible
    * created for HTML:input@type="checkbox" will process

--- a/accessible/tests/browser/e10s/browser_caching_value.js
+++ b/accessible/tests/browser/e10s/browser_caching_value.js
@@ -79,17 +79,17 @@ const valueTests = [
     desc:
       "Value should change to @aria-valuetext when @aria-valuenow is removed",
     id: "slider",
     attrs: [
       {
         attr: "aria-valuenow",
       },
     ],
-    expected: ["hey!", 0, 0, 7, 0],
+    expected: ["hey!", 3.5, 0, 7, 0],
   },
   {
     desc: "Initially value is not set for combobox",
     id: "combobox",
     expected: "",
   },
   {
     desc: "Value should change when @value attribute is updated",

--- a/accessible/tests/mochitest/events/test_valuechange.html
+++ b/accessible/tests/mochitest/events/test_valuechange.html
@@ -133,17 +133,17 @@
     }
 
     // enableLogging("DOMEvents");
     // gA11yEventDumpToConsole = true;
     function doTests() {
       // Test initial values
       testValue("slider_vn", "5", 5, 0, 1000, 0);
       testValue("slider_vnvt", "plain", 0, 0, 5, 0);
-      testValue("slider_vt", "hi", 0, 0, 3, 0);
+      testValue("slider_vt", "hi", 1.5, 0, 3, 0);
       testValue("scrollbar", "5", 5, 0, 1000, 0);
       testValue("splitter", "5", 5, 0, 1000, 0);
       testValue("progress", "22%", 22, 0, 100, 0);
       testValue("range", "6", 6, 0, 10, 1);
 
       // Test that elements which should not expose values do not
       var accSeparator = getAccessible("separator", [nsIAccessibleValue], null, DONOTFAIL_IF_NO_INTERFACE);
       ok(!accSeparator, "value interface is not exposed for separator");

--- a/accessible/tests/mochitest/role/test_aria.html
+++ b/accessible/tests/mochitest/role/test_aria.html
@@ -253,17 +253,17 @@
   <span id="aria_presentation" role="presentation" tabindex="0"/>
   <span id="aria_progressbar" role="progressbar"/>
   <span id="aria_radio" role="radio"/>
   <span id="aria_radiogroup" role="radiogroup"/>
   <span id="aria_region_no_name" role="region"/>
   <span id="aria_region_has_label" role="region" aria-label="label"/>
   <span id="aria_region_has_labelledby" role="region" aria-labelledby="label"/><span id="label" aria-label="label">
   <span id="aria_region_has_title" role="region" title="title"/>
-  <span id="aria_region_empty_name" role="region" aria-label="" title="" aria-labelledby="empty"/><span id="empty"/>
+  <span id="aria_region_empty_name" role="region" aria-label="" title="" aria-labelledby="empty"></span><span id="empty"></span>
   <span id="aria_row" role="row"/>
   <span id="aria_rowheader" role="rowheader"/>
   <span id="aria_scrollbar" role="scrollbar"/>
   <span id="aria_searchbox" role="textbox"/>
   <span id="aria_separator" role="separator"/>
   <span id="aria_slider" role="slider"/>
   <span id="aria_spinbutton" role="spinbutton"/>
   <span id="aria_status" role="status"/>

--- a/accessible/tests/mochitest/value/a11y.ini
+++ b/accessible/tests/mochitest/value/a11y.ini
@@ -1,8 +1,9 @@
 [DEFAULT]
 support-files =
   !/accessible/tests/mochitest/*.js
 
+[test_ariavalue.html]
 [test_general.html]
 [test_number.html]
 [test_progress.html]
 [test_range.html]

new file mode 100644
--- /dev/null
+++ b/accessible/tests/mochitest/value/test_ariavalue.html
@@ -0,0 +1,68 @@
+<html>
+
+<head>
+  <title>nsIAccessible value testing for implicit aria-value* attributes</title>
+
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css" />
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+
+  <script type="application/javascript" src="../common.js"></script>
+  <script type="application/javascript" src="../value.js"></script>
+
+  <script src="chrome://mochikit/content/chrome-harness.js"></script>
+
+  <script type="application/javascript">
+    function doTest() {
+      for (const role of ["slider", "scrollbar"]) {
+        testValue(`${role}_default`, "50", 50, 0, 100, 0);
+        testValue(`${role}_min1max50`, "25.5", 25.5, 1, 50, 0);
+        testValue(`${role}_max200`, "100", 100, 0, 200, 0);
+        testValue(`${role}_min10`, "55", 55, 10, 100, 0);
+        testValue(`${role}_vt`, "juice", 50, 0, 100, 0);
+        testValue(`${role}_vn`, "6", 6, 0, 100, 0);
+        testValue(`${role}_vtvn`, "juice", 6, 0, 100, 0);
+      }
+
+      SimpleTest.finish();
+    }
+
+    SimpleTest.waitForExplicitFinish();
+    addA11yLoadEvent(doTest);
+  </script>
+
+</head>
+
+<body>
+
+  <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1357071"
+    title="Add support for implicit values for aria-value* attributes for scrollbar and slider roles">
+    Bug 1357071
+  </a>
+
+  <p id="display"></p>
+  <div id="content" style="display: none">
+  </div>
+  <pre id="test">
+  </pre>
+
+  <!-- ARIA sliders -->
+  <div id="slider_default" role="slider">vanilla slider</div>
+  <div id="slider_min1max50" role="slider" aria-valuemin="1" aria-valuemax="50">banana slider</div>
+  <div id="slider_max200" role="slider" aria-valuemax="200">cherry slider</div>
+  <div id="slider_min10" role="slider" aria-valuemin="10">strawberry slider</div>
+  <div id="slider_vt" role="slider" aria-valuetext="juice">orange slider</div>
+  <div id="slider_vn" role="slider" aria-valuenow="6">chocolate slider</div>
+  <div id="slider_vtvn" role="slider" aria-valuetext="juice" aria-valuenow="6">apple slider</div>
+
+  <!-- ARIA scrollbars -->
+  <div id="scrollbar_default" role="scrollbar">vanilla scrollbar</div>
+  <div id="scrollbar_min1max50" role="scrollbar" aria-valuemin="1" aria-valuemax="50">banana scrollbar</div>
+  <div id="scrollbar_max200" role="scrollbar" aria-valuemax="200">cherry scrollbar</div>
+  <div id="scrollbar_min10" role="scrollbar" aria-valuemin="10">strawberry scrollbar</div>
+  <div id="scrollbar_vt" role="scrollbar" aria-valuetext="juice">orange scrollbar</div>
+  <div id="scrollbar_vn" role="scrollbar" aria-valuenow="6">chocolate scrollbar</div>
+  <div id="scrollbar_vtvn" role="scrollbar" aria-valuetext="juice" aria-valuenow="6">apple scrollbar</div>
+</body>
+
+</html>