--- a/dom/events/TextComposition.cpp
+++ b/dom/events/TextComposition.cpp
@@ -434,16 +434,22 @@ TextComposition::HandleSelectionEvent(ns
   handler.OnSelectionEvent(aSelectionEvent);
 }
 
 uint32_t
 TextComposition::GetSelectionStartOffset()
 {
   nsCOMPtr<nsIWidget> widget = mPresContext->GetRootWidget();
   WidgetQueryContentEvent selectedTextEvent(true, eQuerySelectedText, widget);
+  if (mRanges && mRanges->HasClauses()) {
+    selectedTextEvent.InitForQuerySelectedText(
+                        ToSelectionType(mRanges->GetFirstClause()->mRangeType));
+  } else {
+    selectedTextEvent.InitForQuerySelectedText(SelectionType::eNormal);
+  }
 
   // The editor which has this composition is observed by active
   // IMEContentObserver, we can use the cache of it.
   RefPtr<IMEContentObserver> contentObserver =
     IMEStateManager::GetActiveContentObserver();
   bool doQuerySelection = true;
   if (contentObserver) {
     if (contentObserver->IsManaging(this)) {

--- a/widget/TextRange.h
+++ b/widget/TextRange.h
@@ -270,22 +270,45 @@ public:
     for (const TextRange& range : *this) {
       if (range.mRangeType == TextRangeType::eCaret) {
         return true;
       }
     }
     return false;
   }
 
+  bool HasClauses() const
+  {
+    for (const TextRange& range : *this) {
+      if (range.IsClause()) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   uint32_t GetCaretPosition() const
   {
     for (const TextRange& range : *this) {
       if (range.mRangeType == TextRangeType::eCaret) {
         return range.mStartOffset;
       }
     }
     return UINT32_MAX;
   }
+
+  const TextRange* GetFirstClause() const
+  {
+    for (const TextRange& range : *this) {
+      // Look for the range of a clause whose start offset is 0 because the
+      // first clause's start offset is always 0.
+      if (range.IsClause() && !range.mStartOffset) {
+        return ⦥
+      }
+    }
+    MOZ_ASSERT(!HasClauses());
+    return nullptr;
+  }
 };
 
 } // namespace mozilla
 
 #endif // mozilla_TextRage_h_