diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index 59a27f7e799b..85d0099c0bcc 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -9928,8 +9928,9 @@ nsDocShell::InternalLoad(nsIURI* aURI,
     isTargetTopLevelDocShell = true;
   }
 
-  // If there's no targetDocShell, that means we are about to create a new window,
-  // perform a content policy check before creating the window.
+  // If there's no targetDocShell, that means we are about to create a new
+  // window (or aWindowTarget is empty). Perform a content policy check before
+  // creating the window.
   if (!targetDocShell) {
     nsCOMPtr<Element> requestingElement;
     nsISupports* requestingContext = nullptr;
@@ -10741,16 +10742,17 @@ nsDocShell::InternalLoad(nsIURI* aURI,
   // mLSHE for the real page.
   if (mLoadType != LOAD_ERROR_PAGE) {
     SetHistoryEntry(&mLSHE, aSHEntry);
+    if (aSHEntry) {
+      // We're making history navigation or a reload. Make sure our history ID
+      // points to the same ID as SHEntry's docshell ID.
+      mHistoryID = aSHEntry->DocshellID();
+    }
   }
 
   mSavingOldViewer = savePresentation;
 
   // If we have a saved content viewer in history, restore and show it now.
   if (aSHEntry && (mLoadType & LOAD_CMD_HISTORY)) {
-    // Make sure our history ID points to the same ID as
-    // SHEntry's docshell ID.
-    mHistoryID = aSHEntry->DocshellID();
-
     // It's possible that the previous viewer of mContentViewer is the
     // viewer that will end up in aSHEntry when it gets closed.  If that's
     // the case, we need to go ahead and force it into its shentry so we
diff --git a/docshell/base/nsDocShell.h b/docshell/base/nsDocShell.h
index 83b73c5fa067..3399c4b73118 100644
--- a/docshell/base/nsDocShell.h
+++ b/docshell/base/nsDocShell.h
@@ -927,7 +927,8 @@ protected:
   int32_t mItemType;
 
   // Index into the SHTransaction list, indicating the previous and current
-  // transaction at the time that this DocShell begins to load
+  // transaction at the time that this DocShell begins to load. Consequently
+  // root docshell's indices can differ from child docshells'.
   int32_t mPreviousTransIndex;
   int32_t mLoadedTransIndex;