--- a/ipc/glue/BackgroundUtils.cpp
+++ b/ipc/glue/BackgroundUtils.cpp
@@ -382,16 +382,17 @@ LoadInfoToLoadInfoArgs(nsILoadInfo *aLoa
       static_cast<uint32_t>(aLoadInfo->GetTainting()),
       aLoadInfo->GetUpgradeInsecureRequests(),
       aLoadInfo->GetVerifySignedContent(),
       aLoadInfo->GetEnforceSRI(),
       aLoadInfo->GetForceInheritPrincipalDropped(),
       aLoadInfo->GetInnerWindowID(),
       aLoadInfo->GetOuterWindowID(),
       aLoadInfo->GetParentOuterWindowID(),
+      aLoadInfo->GetTopOuterWindowID(),
       aLoadInfo->GetFrameOuterWindowID(),
       aLoadInfo->GetEnforceSecurity(),
       aLoadInfo->GetInitialSecurityCheckDone(),
       aLoadInfo->GetIsInThirdPartyContext(),
       aLoadInfo->GetOriginAttributes(),
       redirectChainIncludingInternalRedirects,
       redirectChain,
       aLoadInfo->CorsUnsafeHeaders(),
@@ -477,16 +478,17 @@ LoadInfoArgsToLoadInfo(const OptionalLoa
                           static_cast<LoadTainting>(loadInfoArgs.tainting()),
                           loadInfoArgs.upgradeInsecureRequests(),
                           loadInfoArgs.verifySignedContent(),
                           loadInfoArgs.enforceSRI(),
                           loadInfoArgs.forceInheritPrincipalDropped(),
                           loadInfoArgs.innerWindowID(),
                           loadInfoArgs.outerWindowID(),
                           loadInfoArgs.parentOuterWindowID(),
+                          loadInfoArgs.topOuterWindowID(),
                           loadInfoArgs.frameOuterWindowID(),
                           loadInfoArgs.enforceSecurity(),
                           loadInfoArgs.initialSecurityCheckDone(),
                           loadInfoArgs.isInThirdPartyContext(),
                           loadInfoArgs.originAttributes(),
                           redirectChainIncludingInternalRedirects,
                           redirectChain,
                           loadInfoArgs.corsUnsafeHeaders(),

--- a/netwerk/base/LoadInfo.cpp
+++ b/netwerk/base/LoadInfo.cpp
@@ -24,16 +24,26 @@
 #include "NullPrincipal.h"
 #include "nsRedirectHistoryEntry.h"
 
 using namespace mozilla::dom;
 
 namespace mozilla {
 namespace net {
 
+uint64_t
+FindTopOuterWindowID(nsPIDOMWindowOuter* aOuter)
+{
+  nsCOMPtr<nsPIDOMWindowOuter> outer = aOuter;
+  while (nsCOMPtr<nsPIDOMWindowOuter> parent = outer->GetScriptableParentOrNull()) {
+    outer = parent;
+  }
+  return outer->WindowID();
+}
+
 LoadInfo::LoadInfo(nsIPrincipal* aLoadingPrincipal,
                    nsIPrincipal* aTriggeringPrincipal,
                    nsINode* aLoadingContext,
                    nsSecurityFlags aSecurityFlags,
                    nsContentPolicyType aContentPolicyType)
   : mLoadingPrincipal(aLoadingContext ?
                         aLoadingContext->NodePrincipal() : aLoadingPrincipal)
   , mTriggeringPrincipal(aTriggeringPrincipal ?
@@ -45,16 +55,17 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadin
   , mTainting(LoadTainting::Basic)
   , mUpgradeInsecureRequests(false)
   , mVerifySignedContent(false)
   , mEnforceSRI(false)
   , mForceInheritPrincipalDropped(false)
   , mInnerWindowID(0)
   , mOuterWindowID(0)
   , mParentOuterWindowID(0)
+  , mTopOuterWindowID(0)
   , mFrameOuterWindowID(0)
   , mEnforceSecurity(false)
   , mInitialSecurityCheckDone(false)
   , mIsThirdPartyContext(false)
   , mForcePreflight(false)
   , mIsPreflight(false)
   , mForceHSTSPriming(false)
   , mMixedContentWouldBlock(false)
@@ -97,16 +108,17 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadin
 
   if (aLoadingContext) {
     nsCOMPtr<nsPIDOMWindowOuter> contextOuter = aLoadingContext->OwnerDoc()->GetWindow();
     if (contextOuter) {
       ComputeIsThirdPartyContext(contextOuter);
       mOuterWindowID = contextOuter->WindowID();
       nsCOMPtr<nsPIDOMWindowOuter> parent = contextOuter->GetScriptableParent();
       mParentOuterWindowID = parent ? parent->WindowID() : mOuterWindowID;
+      mTopOuterWindowID = FindTopOuterWindowID(contextOuter);
     }
 
     mInnerWindowID = aLoadingContext->OwnerDoc()->InnerWindowID();
 
     // When the element being loaded is a frame, we choose the frame's window
     // for the window ID and the frame element's window as the parent
     // window. This is the behavior that Chrome exposes to add-ons.
     // NB: If the frameLoaderOwner doesn't have a frame loader, then the load
@@ -220,16 +232,17 @@ LoadInfo::LoadInfo(nsPIDOMWindowOuter* a
   , mTainting(LoadTainting::Basic)
   , mUpgradeInsecureRequests(false)
   , mVerifySignedContent(false)
   , mEnforceSRI(false)
   , mForceInheritPrincipalDropped(false)
   , mInnerWindowID(0)
   , mOuterWindowID(0)
   , mParentOuterWindowID(0)
+  , mTopOuterWindowID(0)
   , mFrameOuterWindowID(0)
   , mEnforceSecurity(false)
   , mInitialSecurityCheckDone(false)
   , mIsThirdPartyContext(false) // NB: TYPE_DOCUMENT implies not third-party.
   , mForcePreflight(false)
   , mIsPreflight(false)
   , mForceHSTSPriming(false)
   , mMixedContentWouldBlock(false)
@@ -250,16 +263,17 @@ LoadInfo::LoadInfo(nsPIDOMWindowOuter* a
 
   // NB: Ignore the current inner window since we're navigating away from it.
   mOuterWindowID = aOuterWindow->WindowID();
 
   // TODO We can have a parent without a frame element in some cases dealing
   // with the hidden window.
   nsCOMPtr<nsPIDOMWindowOuter> parent = aOuterWindow->GetScriptableParent();
   mParentOuterWindowID = parent ? parent->WindowID() : 0;
+  mTopOuterWindowID = FindTopOuterWindowID(aOuterWindow);
 
   // get the docshell from the outerwindow, and then get the originattributes
   nsCOMPtr<nsIDocShell> docShell = aOuterWindow->GetDocShell();
   MOZ_ASSERT(docShell);
   mOriginAttributes = nsDocShell::Cast(docShell)->GetOriginAttributes();
 
 #ifdef DEBUG
   if (docShell->ItemType() == nsIDocShellTreeItem::typeChrome) {
@@ -281,16 +295,17 @@ LoadInfo::LoadInfo(const LoadInfo& rhs)
   , mTainting(rhs.mTainting)
   , mUpgradeInsecureRequests(rhs.mUpgradeInsecureRequests)
   , mVerifySignedContent(rhs.mVerifySignedContent)
   , mEnforceSRI(rhs.mEnforceSRI)
   , mForceInheritPrincipalDropped(rhs.mForceInheritPrincipalDropped)
   , mInnerWindowID(rhs.mInnerWindowID)
   , mOuterWindowID(rhs.mOuterWindowID)
   , mParentOuterWindowID(rhs.mParentOuterWindowID)
+  , mTopOuterWindowID(rhs.mTopOuterWindowID)
   , mFrameOuterWindowID(rhs.mFrameOuterWindowID)
   , mEnforceSecurity(rhs.mEnforceSecurity)
   , mInitialSecurityCheckDone(rhs.mInitialSecurityCheckDone)
   , mIsThirdPartyContext(rhs.mIsThirdPartyContext)
   , mOriginAttributes(rhs.mOriginAttributes)
   , mRedirectChainIncludingInternalRedirects(
       rhs.mRedirectChainIncludingInternalRedirects)
   , mRedirectChain(rhs.mRedirectChain)
@@ -314,16 +329,17 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadin
                    LoadTainting aTainting,
                    bool aUpgradeInsecureRequests,
                    bool aVerifySignedContent,
                    bool aEnforceSRI,
                    bool aForceInheritPrincipalDropped,
                    uint64_t aInnerWindowID,
                    uint64_t aOuterWindowID,
                    uint64_t aParentOuterWindowID,
+                   uint64_t aTopOuterWindowID,
                    uint64_t aFrameOuterWindowID,
                    bool aEnforceSecurity,
                    bool aInitialSecurityCheckDone,
                    bool aIsThirdPartyContext,
                    const OriginAttributes& aOriginAttributes,
                    RedirectHistoryArray& aRedirectChainIncludingInternalRedirects,
                    RedirectHistoryArray& aRedirectChain,
                    const nsTArray<nsCString>& aCorsUnsafeHeaders,
@@ -342,16 +358,17 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadin
   , mTainting(aTainting)
   , mUpgradeInsecureRequests(aUpgradeInsecureRequests)
   , mVerifySignedContent(aVerifySignedContent)
   , mEnforceSRI(aEnforceSRI)
   , mForceInheritPrincipalDropped(aForceInheritPrincipalDropped)
   , mInnerWindowID(aInnerWindowID)
   , mOuterWindowID(aOuterWindowID)
   , mParentOuterWindowID(aParentOuterWindowID)
+  , mTopOuterWindowID(aTopOuterWindowID)
   , mFrameOuterWindowID(aFrameOuterWindowID)
   , mEnforceSecurity(aEnforceSecurity)
   , mInitialSecurityCheckDone(aInitialSecurityCheckDone)
   , mIsThirdPartyContext(aIsThirdPartyContext)
   , mOriginAttributes(aOriginAttributes)
   , mCorsUnsafeHeaders(aCorsUnsafeHeaders)
   , mForcePreflight(aForcePreflight)
   , mIsPreflight(aIsPreflight)
@@ -705,16 +722,23 @@ LoadInfo::GetOuterWindowID(uint64_t* aRe
 NS_IMETHODIMP
 LoadInfo::GetParentOuterWindowID(uint64_t* aResult)
 {
   *aResult = mParentOuterWindowID;
   return NS_OK;
 }
 
 NS_IMETHODIMP
+LoadInfo::GetTopOuterWindowID(uint64_t* aResult)
+{
+  *aResult = mTopOuterWindowID;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
 LoadInfo::GetFrameOuterWindowID(uint64_t* aResult)
 {
   *aResult = mFrameOuterWindowID;
   return NS_OK;
 }
 
 NS_IMETHODIMP
 LoadInfo::GetScriptableOriginAttributes(JSContext* aCx,

--- a/netwerk/base/LoadInfo.h
+++ b/netwerk/base/LoadInfo.h
@@ -100,16 +100,17 @@ private:
            LoadTainting aTainting,
            bool aUpgradeInsecureRequests,
            bool aVerifySignedContent,
            bool aEnforceSRI,
            bool aForceInheritPrincipalDropped,
            uint64_t aInnerWindowID,
            uint64_t aOuterWindowID,
            uint64_t aParentOuterWindowID,
+           uint64_t aTopOuterWindowID,
            uint64_t aFrameOuterWindowID,
            bool aEnforceSecurity,
            bool aInitialSecurityCheckDone,
            bool aIsThirdPartyRequest,
            const OriginAttributes& aOriginAttributes,
            RedirectHistoryArray& aRedirectChainIncludingInternalRedirects,
            RedirectHistoryArray& aRedirectChain,
            const nsTArray<nsCString>& aUnsafeHeaders,
@@ -151,16 +152,17 @@ private:
   LoadTainting                     mTainting;
   bool                             mUpgradeInsecureRequests;
   bool                             mVerifySignedContent;
   bool                             mEnforceSRI;
   bool                             mForceInheritPrincipalDropped;
   uint64_t                         mInnerWindowID;
   uint64_t                         mOuterWindowID;
   uint64_t                         mParentOuterWindowID;
+  uint64_t                         mTopOuterWindowID;
   uint64_t                         mFrameOuterWindowID;
   bool                             mEnforceSecurity;
   bool                             mInitialSecurityCheckDone;
   bool                             mIsThirdPartyContext;
   OriginAttributes                 mOriginAttributes;
   RedirectHistoryArray             mRedirectChainIncludingInternalRedirects;
   RedirectHistoryArray             mRedirectChain;
   nsTArray<nsCString>              mCorsUnsafeHeaders;

--- a/netwerk/base/nsILoadInfo.idl
+++ b/netwerk/base/nsILoadInfo.idl
@@ -501,16 +501,17 @@ interface nsILoadInfo : nsISupports
    *
    * Note that these window IDs can be 0 if the window is not
    * available. parentOuterWindowID will be the same as outerWindowID if the
    * window has no parent.
    */
   [infallible] readonly attribute unsigned long long innerWindowID;
   [infallible] readonly attribute unsigned long long outerWindowID;
   [infallible] readonly attribute unsigned long long parentOuterWindowID;
+  [infallible] readonly attribute unsigned long long topOuterWindowID;
 
   /**
    * Only when the element being loaded is <frame src="foo.html">
    * (or, more generally, if the element QIs to nsIFrameLoaderOwner),
    * the frameOuterWindowID is the outer window containing the
    * foo.html document.
    *
    * Note: For other cases, frameOuterWindowID is 0.

--- a/netwerk/ipc/NeckoChannelParams.ipdlh
+++ b/netwerk/ipc/NeckoChannelParams.ipdlh
@@ -46,16 +46,17 @@ struct LoadInfoArgs
   uint32_t                    tainting;
   bool                        upgradeInsecureRequests;
   bool                        verifySignedContent;
   bool                        enforceSRI;
   bool                        forceInheritPrincipalDropped;
   uint64_t                    innerWindowID;
   uint64_t                    outerWindowID;
   uint64_t                    parentOuterWindowID;
+  uint64_t                    topOuterWindowID;
   uint64_t                    frameOuterWindowID;
   bool                        enforceSecurity;
   bool                        initialSecurityCheckDone;
   bool                        isInThirdPartyContext;
   OriginAttributes            originAttributes;
   RedirectHistoryEntryInfo[]  redirectChainIncludingInternalRedirects;
   RedirectHistoryEntryInfo[]  redirectChain;
   nsCString[]                 corsUnsafeHeaders;