diff --git a/ipc/glue/BackgroundUtils.cpp b/ipc/glue/BackgroundUtils.cpp
index 53ff9734e0fd..0fcd83e097eb 100644
--- a/ipc/glue/BackgroundUtils.cpp
+++ b/ipc/glue/BackgroundUtils.cpp
@@ -224,6 +224,10 @@ LoadInfoToLoadInfoArgs(nsILoadInfo *aLoadInfo,
   rv = PrincipalToPrincipalInfo(aLoadInfo->TriggeringPrincipal(),
                                 &triggeringPrincipalInfo);
 
+  PrincipalInfo principalToInheritInfo;
+  rv = PrincipalToPrincipalInfo(aLoadInfo->PrincipalToInherit(),
+                                &principalToInheritInfo);
+
   nsTArray<PrincipalInfo> redirectChainIncludingInternalRedirects;
   for (const nsCOMPtr<nsIPrincipal>& principal : aLoadInfo->RedirectChainIncludingInternalRedirects()) {
     rv = PrincipalToPrincipalInfo(principal, redirectChainIncludingInternalRedirects.AppendElement());
@@ -240,6 +244,7 @@ LoadInfoToLoadInfoArgs(nsILoadInfo *aLoadInfo,
     LoadInfoArgs(
       loadingPrincipalInfo,
       triggeringPrincipalInfo,
+      principalToInheritInfo,
       aLoadInfo->GetSecurityFlags(),
       aLoadInfo->InternalContentPolicyType(),
       static_cast<uint32_t>(aLoadInfo->GetTainting()),
@@ -288,6 +293,10 @@ LoadInfoArgsToLoadInfo(const OptionalLoadInfoArgs& aOptionalLoadInfoArgs,
     PrincipalInfoToPrincipal(loadInfoArgs.triggeringPrincipalInfo(), &rv);
   NS_ENSURE_SUCCESS(rv, rv);
 
+  nsCOMPtr<nsIPrincipal> principalToInherit =
+  PrincipalInfoToPrincipal(loadInfoArgs.principalToInheritInfo(), &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
   nsTArray<nsCOMPtr<nsIPrincipal>> redirectChainIncludingInternalRedirects;
   for (const PrincipalInfo& principalInfo : loadInfoArgs.redirectChainIncludingInternalRedirects()) {
     nsCOMPtr<nsIPrincipal> redirectedPrincipal =
@@ -307,6 +316,7 @@ LoadInfoArgsToLoadInfo(const OptionalLoadInfoArgs& aOptionalLoadInfoArgs,
   nsCOMPtr<nsILoadInfo> loadInfo =
     new mozilla::LoadInfo(loadingPrincipal,
                           triggeringPrincipal,
+                          principalToInherit,
                           loadInfoArgs.securityFlags(),
                           loadInfoArgs.contentPolicyType(),
                           static_cast<LoadTainting>(loadInfoArgs.tainting()),
diff --git a/netwerk/base/LoadInfo.cpp b/netwerk/base/LoadInfo.cpp
index 1e33df471a77..6ce2bf1c1b72 100644
--- a/netwerk/base/LoadInfo.cpp
+++ b/netwerk/base/LoadInfo.cpp
@@ -44,6 +44,7 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadingPrincipal,
                         aLoadingContext->NodePrincipal() : aLoadingPrincipal)
   , mTriggeringPrincipal(aTriggeringPrincipal ?
                            aTriggeringPrincipal : mLoadingPrincipal.get())
+  , mPrincipalToInherit(mTriggeringPrincipal)
   , mLoadingContext(do_GetWeakReference(aLoadingContext))
   , mSecurityFlags(aSecurityFlags)
   , mInternalContentPolicyType(aContentPolicyType)
@@ -64,6 +65,7 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadingPrincipal,
 {
   MOZ_ASSERT(mLoadingPrincipal);
   MOZ_ASSERT(mTriggeringPrincipal);
+  MOZ_ASSERT(mPrincipalToInherit);
 
 #ifdef DEBUG
   // TYPE_DOCUMENT loads initiated by javascript tests will go through
@@ -214,6 +216,7 @@ LoadInfo::LoadInfo(nsPIDOMWindowOuter* aOuterWindow,
                    nsSecurityFlags aSecurityFlags)
   : mLoadingPrincipal(nullptr)
   , mTriggeringPrincipal(aTriggeringPrincipal)
+  , mPrincipalToInherit(mTriggeringPrincipal)
   , mSecurityFlags(aSecurityFlags)
   , mInternalContentPolicyType(nsIContentPolicy::TYPE_DOCUMENT)
   , mTainting(LoadTainting::Basic)
@@ -235,6 +238,7 @@ LoadInfo::LoadInfo(nsPIDOMWindowOuter* aOuterWindow,
   // Grab the information we can out of the window.
   MOZ_ASSERT(aOuterWindow);
   MOZ_ASSERT(mTriggeringPrincipal);
+  MOZ_ASSERT(mPrincipalToInherit);
 
   // if the load is sandboxed, we can not also inherit the principal
   if (mSecurityFlags & nsILoadInfo::SEC_SANDBOXED) {
@@ -270,6 +274,7 @@ LoadInfo::LoadInfo(nsPIDOMWindowOuter* aOuterWindow,
 LoadInfo::LoadInfo(const LoadInfo& rhs)
   : mLoadingPrincipal(rhs.mLoadingPrincipal)
   , mTriggeringPrincipal(rhs.mTriggeringPrincipal)
+  , mPrincipalToInherit(rhs.mPrincipalToInherit)
   , mLoadingContext(rhs.mLoadingContext)
   , mSecurityFlags(rhs.mSecurityFlags)
   , mInternalContentPolicyType(rhs.mInternalContentPolicyType)
@@ -297,6 +302,7 @@ LoadInfo::LoadInfo(const LoadInfo& rhs)
 
 LoadInfo::LoadInfo(nsIPrincipal* aLoadingPrincipal,
                    nsIPrincipal* aTriggeringPrincipal,
+                   nsIPrincipal* aPrincipalToInherit,
                    nsSecurityFlags aSecurityFlags,
                    nsContentPolicyType aContentPolicyType,
                    LoadTainting aTainting,
@@ -319,6 +325,7 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadingPrincipal,
                    bool aIsPreflight)
   : mLoadingPrincipal(aLoadingPrincipal)
   , mTriggeringPrincipal(aTriggeringPrincipal)
+  , mPrincipalToInherit(aPrincipalToInherit)
   , mSecurityFlags(aSecurityFlags)
   , mInternalContentPolicyType(aContentPolicyType)
   , mTainting(aTainting)
@@ -341,6 +348,7 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadingPrincipal,
   // Only top level TYPE_DOCUMENT loads can have a null loadingPrincipal
   MOZ_ASSERT(mLoadingPrincipal || aContentPolicyType == nsIContentPolicy::TYPE_DOCUMENT);
   MOZ_ASSERT(mTriggeringPrincipal);
+  MOZ_ASSERT(mPrincipalToInherit);
 
   mRedirectChainIncludingInternalRedirects.SwapElements(
     aRedirectChainIncludingInternalRedirects);
@@ -425,6 +433,27 @@ LoadInfo::TriggeringPrincipal()
   return mTriggeringPrincipal;
 }
 
+NS_IMETHODIMP
+LoadInfo::GetPrincipalToInherit(nsIPrincipal** aPrincipalToInherit)
+{
+  NS_ADDREF(*aPrincipalToInherit = mPrincipalToInherit);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+LoadInfo::SetPrincipalToInherit(nsIPrincipal* aPrincipalToInherit)
+{
+  MOZ_ASSERT(aPrincipalToInherit, "must be a valid principal to inherit");
+  mPrincipalToInherit = aPrincipalToInherit;
+  return NS_OK;
+}
+
+nsIPrincipal*
+LoadInfo::PrincipalToInherit()
+{
+  return mPrincipalToInherit;
+}
+
 NS_IMETHODIMP
 LoadInfo::GetLoadingDocument(nsIDOMDocument** aResult)
 {
diff --git a/netwerk/base/LoadInfo.h b/netwerk/base/LoadInfo.h
index 0f407d449ec4..8d90beb53378 100644
--- a/netwerk/base/LoadInfo.h
+++ b/netwerk/base/LoadInfo.h
@@ -86,6 +86,7 @@ private:
   // Please note that aRedirectChain uses swapElements.
   LoadInfo(nsIPrincipal* aLoadingPrincipal,
            nsIPrincipal* aTriggeringPrincipal,
+           nsIPrincipal* aPrincipalToInherit,
            nsSecurityFlags aSecurityFlags,
            nsContentPolicyType aContentPolicyType,
            LoadTainting aTainting,
@@ -126,6 +127,7 @@ private:
   // if you add a member, please also update the copy constructor
   nsCOMPtr<nsIPrincipal>           mLoadingPrincipal;
   nsCOMPtr<nsIPrincipal>           mTriggeringPrincipal;
+  nsCOMPtr<nsIPrincipal>           mPrincipalToInherit;
   nsWeakPtr                        mLoadingContext;
   nsSecurityFlags                  mSecurityFlags;
   nsContentPolicyType              mInternalContentPolicyType;
diff --git a/netwerk/base/nsILoadInfo.idl b/netwerk/base/nsILoadInfo.idl
index 3cb7c18189cb..6894aa565e3b 100644
--- a/netwerk/base/nsILoadInfo.idl
+++ b/netwerk/base/nsILoadInfo.idl
@@ -246,6 +246,19 @@ interface nsILoadInfo : nsISupports
   [noscript, notxpcom, nostdcall, binaryname(TriggeringPrincipal)]
   nsIPrincipal binaryTriggeringPrincipal();
 
+  /**
+   * The principalToInherit is the principal that is used when the inherit flag
+   * is set. For loads that are not TYPE_DOCUMENT or TYPE_SUBDOCUMENT that
+   * principal is always identical to the triggeringPrincipal.
+   */
+  attribute nsIPrincipal principalToInherit;
+
+  /**
+   * A C++-friendly version of principalToInherit.
+   */
+  [noscript, notxpcom, nostdcall, binaryname(PrincipalToInherit)]
+  nsIPrincipal binaryPrincipalToInherit();
+
   /**
    * This is the ownerDocument of the LoadingNode. Unless the LoadingNode
    * is a Document, in which case the LoadingDocument is the same as the
diff --git a/netwerk/ipc/NeckoChannelParams.ipdlh b/netwerk/ipc/NeckoChannelParams.ipdlh
index 477f959c44d8..6bc287182ed8 100644
--- a/netwerk/ipc/NeckoChannelParams.ipdlh
+++ b/netwerk/ipc/NeckoChannelParams.ipdlh
@@ -30,6 +30,7 @@ struct LoadInfoArgs
 {
   OptionalPrincipalInfo requestingPrincipalInfo;
   PrincipalInfo         triggeringPrincipalInfo;
+  PrincipalInfo         principalToInheritInfo;
   uint32_t              securityFlags;
   uint32_t              contentPolicyType;
   uint32_t              tainting;