--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -9914,18 +9914,19 @@ nsDocShell::InternalLoad(nsIURI* aURI,
       // an iframe since that's more common.
       contentType = nsIContentPolicy::TYPE_INTERNAL_IFRAME;
     }
   } else {
     contentType = nsIContentPolicy::TYPE_DOCUMENT;
     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;
 
     if (contentType == nsIContentPolicy::TYPE_DOCUMENT) {
       if (XRE_IsContentProcess()) {
         // In e10s the child process doesn't have access to the element that
         // contains the browsing context (because that element is in the chrome
@@ -10727,26 +10728,27 @@ nsDocShell::InternalLoad(nsIURI* aURI,
 
   mLoadType = aLoadType;
 
   // mLSHE should be assigned to aSHEntry, only after Stop() has
   // been called. But when loading an error page, do not clear the
   // 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
     // can restore it.
     if (mContentViewer) {
       nsCOMPtr<nsIContentViewer> prevViewer;
       mContentViewer->GetPreviousViewer(getter_AddRefs(prevViewer));
       if (prevViewer) {

--- a/docshell/base/nsDocShell.h
+++ b/docshell/base/nsDocShell.h
@@ -920,17 +920,18 @@ protected:
   int32_t mMarginWidth;
   int32_t mMarginHeight;
 
   // This can either be a content docshell or a chrome docshell. After
   // Create() is called, the type is not expected to change.
   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;
 
   uint32_t mSandboxFlags;
   nsWeakPtr mOnePermittedSandboxedNavigator;
 
   // The orientation lock as described by
   // https://w3c.github.io/screen-orientation/