--- a/accessible/ipc/extension/mac/DocAccessiblePlatformExtChild.cpp
+++ b/accessible/ipc/extension/mac/DocAccessiblePlatformExtChild.cpp
@@ -126,16 +126,29 @@ mozilla::ipc::IPCResult DocAccessiblePla
     return IPC_OK();
   }
 
   *aBounds = acc->BoundsForRange(aStartOffset, endContainer, aEndOffset);
 
   return IPC_OK();
 }
 
+mozilla::ipc::IPCResult DocAccessiblePlatformExtChild::RecvLengthForRange(
+    const uint64_t& aID, const int32_t& aStartOffset,
+    const uint64_t& aEndContainer, const int32_t& aEndOffset,
+    int32_t* aLength) {
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult DocAccessiblePlatformExtChild::RecvOffsetAtIndex(
+    const uint64_t& aID, const int32_t& aIndex, uint64_t* aContainer,
+    int32_t* aOffset) {
+  return IPC_OK();
+}
+
 HyperTextAccessibleWrap*
 DocAccessiblePlatformExtChild::IdToHyperTextAccessibleWrap(
     const uint64_t& aID) const {
   return static_cast<HyperTextAccessibleWrap*>(
       static_cast<DocAccessibleChild*>(Manager())->IdToHyperTextAccessible(
           aID));
 }
 

--- a/accessible/ipc/extension/mac/DocAccessiblePlatformExtChild.h
+++ b/accessible/ipc/extension/mac/DocAccessiblePlatformExtChild.h
@@ -41,16 +41,27 @@ class DocAccessiblePlatformExtChild : pu
                                            nsString* aText);
 
   mozilla::ipc::IPCResult RecvBoundsForRange(const uint64_t& aID,
                                              const int32_t& aStartOffset,
                                              const uint64_t& aEndContainer,
                                              const int32_t& aEndOffset,
                                              nsIntRect* aBounds);
 
+  mozilla::ipc::IPCResult RecvLengthForRange(const uint64_t& aID,
+                                             const int32_t& aStartOffset,
+                                             const uint64_t& aEndContainer,
+                                             const int32_t& aEndOffset,
+                                             int32_t* aLength);
+
+  mozilla::ipc::IPCResult RecvOffsetAtIndex(const uint64_t& aID,
+                                            const int32_t& aIndex,
+                                            uint64_t* aContainer,
+                                            int32_t* aOffset);
+
  private:
   HyperTextAccessibleWrap* IdToHyperTextAccessibleWrap(
       const uint64_t& aID) const;
 };
 }  // namespace a11y
 }  // namespace mozilla
 
 #endif

--- a/accessible/ipc/extension/mac/PDocAccessiblePlatformExt.ipdl
+++ b/accessible/ipc/extension/mac/PDocAccessiblePlatformExt.ipdl
@@ -31,12 +31,19 @@ child:
   nested(inside_sync) sync PreviousClusterAt(uint64_t aID, int32_t aOffset)
       returns(uint64_t aNextContainer, int32_t aNextOffset);
 
   nested(inside_sync) sync TextForRange(uint64_t aID, int32_t aStartOffset, uint64_t aEndContainer, int32_t aEndOffset)
       returns(nsString aText);
 
   nested(inside_sync) sync BoundsForRange(uint64_t aID, int32_t aStartOffset, uint64_t aEndContainer, int32_t aEndOffset)
       returns(nsIntRect aRetVal);
+
+  nested(inside_sync) sync LengthForRange(uint64_t aID, int32_t aStartOffset, uint64_t aEndContainer, int32_t aEndOffset)
+      returns(int32_t aLength);
+
+  nested(inside_sync) sync OffsetAtIndex(uint64_t aID, int32_t aIndex)
+      returns(uint64_t aContainer, int32_t aOffset);
+
 };
 
 }  // namespace a11y
 }  // namespace mozilla

--- a/ipc/ipdl/sync-messages.ini
+++ b/ipc/ipdl/sync-messages.ini
@@ -627,16 +627,22 @@ platform = mac
 description = Retrieve previous character from offset. Platform API is synchronous, so this needs to be too.
 platform = mac
 [PDocAccessiblePlatformExt::TextForRange]
 description = Retrieve flattened string for text range. Platform API is synchronous, so this needs to be too.
 platform = mac
 [PDocAccessiblePlatformExt::BoundsForRange]
 description = Retrieve geometric bounds for text range. Platform API is synchronous, so this needs to be too.
 platform = mac
+[PDocAccessiblePlatformExt::LengthForRange]
+description = Retrieve length of text range. Platform API is synchronous, so this needs to be too.
+platform = mac
+[PDocAccessiblePlatformExt::OffsetAtIndex]
+description = Retrieve text offset at absolute index. Platform API is synchronous, so this needs to be too.
+platform = mac
 
 # Plugins
 [PPluginWidget::Create]
 description = Legacy NPAPI IPC
 [PPluginWidget::GetNativePluginPort]
 description = Legacy NPAPI IPC
 [PPluginWidget::SetNativeChildWindow]
 description = Legacy NPAPI IPC