diff --git a/accessible/base/CacheConstants.h b/accessible/base/CacheConstants.h
index 58ce94aa5407..d4440a03a204 100644
--- a/accessible/base/CacheConstants.h
+++ b/accessible/base/CacheConstants.h
@@ -69,6 +69,10 @@ static constexpr RelationData kRelationTypeAtoms[] = {
      RelationType::LABEL_FOR},
     {nsGkAtoms::_for, nsGkAtoms::label, RelationType::LABEL_FOR,
      RelationType::LABELLED_BY},
+    {nsGkAtoms::aria_controls, nullptr, RelationType::CONTROLLER_FOR,
+     RelationType::CONTROLLED_BY},
+    {nsGkAtoms::_for, nsGkAtoms::output, RelationType::CONTROLLED_BY,
+     RelationType::CONTROLLER_FOR},
 };
 
 }  // namespace a11y
diff --git a/accessible/generic/LocalAccessible.cpp b/accessible/generic/LocalAccessible.cpp
index 09c3656014a4..8bcfa5f7aee5 100644
--- a/accessible/generic/LocalAccessible.cpp
+++ b/accessible/generic/LocalAccessible.cpp
@@ -1374,6 +1374,10 @@ void LocalAccessible::DOMAttributeChanged(int32_t aNameSpaceID,
     SendCache(CacheDomain::Actions, CacheUpdateType::Update);
   }
 
+  if (aAttribute == nsGkAtoms::aria_controls) {
+    mDoc->QueueCacheUpdate(this, CacheDomain::Relations);
+  }
+
   if (aAttribute == nsGkAtoms::alt &&
       !elm->HasAttr(kNameSpaceID_None, nsGkAtoms::aria_label) &&
       !elm->HasAttr(kNameSpaceID_None, nsGkAtoms::aria_labelledby)) {
diff --git a/accessible/html/HTMLElementAccessibles.cpp b/accessible/html/HTMLElementAccessibles.cpp
index 3398e59b22e3..518506fe753c 100644
--- a/accessible/html/HTMLElementAccessibles.cpp
+++ b/accessible/html/HTMLElementAccessibles.cpp
@@ -96,6 +96,19 @@ Relation HTMLOutputAccessible::RelationByType(RelationType aType) const {
   return rel;
 }
 
+void HTMLOutputAccessible::DOMAttributeChanged(int32_t aNameSpaceID,
+                                               nsAtom* aAttribute,
+                                               int32_t aModType,
+                                               const nsAttrValue* aOldValue,
+                                               uint64_t aOldState) {
+  HyperTextAccessibleWrap::DOMAttributeChanged(aNameSpaceID, aAttribute,
+                                               aModType, aOldValue, aOldState);
+
+  if (aAttribute == nsGkAtoms::_for) {
+    mDoc->QueueCacheUpdate(this, CacheDomain::Relations);
+  }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // HTMLSummaryAccessible
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/accessible/html/HTMLElementAccessibles.h b/accessible/html/HTMLElementAccessibles.h
index fdae42db2d07..b45e94591203 100644
--- a/accessible/html/HTMLElementAccessibles.h
+++ b/accessible/html/HTMLElementAccessibles.h
@@ -84,6 +84,11 @@ class HTMLOutputAccessible : public HyperTextAccessibleWrap {
   // LocalAccessible
   virtual Relation RelationByType(RelationType aType) const override;
 
+  virtual void DOMAttributeChanged(int32_t aNameSpaceID, nsAtom* aAttribute,
+                                   int32_t aModType,
+                                   const nsAttrValue* aOldValue,
+                                   uint64_t aOldState) override;
+
  protected:
   virtual ~HTMLOutputAccessible() {}
 };
diff --git a/accessible/tests/browser/e10s/browser_caching_relations.js b/accessible/tests/browser/e10s/browser_caching_relations.js
index b56b19462ba9..ddaf26c708f6 100644
--- a/accessible/tests/browser/e10s/browser_caching_relations.js
+++ b/accessible/tests/browser/e10s/browser_caching_relations.js
@@ -226,3 +226,25 @@ addAccessibleTask(
   },
   { iframe: true, remoteIframe: true }
 );
+
+/**
+ * Test caching of relations with respect to output objects and their "for" attr.
+ */
+addAccessibleTask(
+  `
+  <form oninput="host.value=parseInt(dependant1.value)+parseInt(dependant2.value)">
+    <input type="number" id="dependant1" value="50"> +
+    <input type="number" id="dependant2" value="25"> =
+    <output name="host" id="host"></output>
+  </form>`,
+  async function(browser, accDoc) {
+    await testRelated(
+      browser,
+      accDoc,
+      "for",
+      RELATION_CONTROLLED_BY,
+      RELATION_CONTROLLER_FOR
+    );
+  },
+  { iframe: true, remoteIframe: true }
+);