diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index aff9c9a9bd9..1ea89ea71c0 100755
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -142,6 +142,7 @@
 #include "nsIXULRuntime.h"
 #include "gfxDrawable.h"
 #include "ImageOps.h"
+#include "mozilla/dom/nsMixedContentBlocker.h"
 #include "nsMemoryInfoDumper.h"
 #include "nsMemoryReporterManager.h"
 #include "nsServiceManagerUtils.h"
@@ -4175,6 +4176,17 @@ ContentParent::RecvIsSecureURI(const uint32_t& type,
     return NS_SUCCEEDED(rv);
 }
 
+bool
+ContentParent::RecvAccumulateMixedContentHSTS(const URIParams& aURI, const bool& aActive)
+{
+    nsCOMPtr<nsIURI> ourURI = DeserializeURI(aURI);
+    if (!ourURI) {
+        return false;
+    }
+    nsMixedContentBlocker::AccumulateMixedContentHSTS(ourURI, aActive);
+    return true;
+}
+
 bool
 ContentParent::RecvLoadURIExternal(const URIParams& uri)
 {
diff --git a/dom/ipc/ContentParent.h b/dom/ipc/ContentParent.h
index ac881edeea0..d65cdca423e 100644
--- a/dom/ipc/ContentParent.h
+++ b/dom/ipc/ContentParent.h
@@ -626,6 +626,8 @@ private:
     virtual bool RecvIsSecureURI(const uint32_t& aType, const URIParams& aURI,
                                  const uint32_t& aFlags, bool* aIsSecureURI) override;
 
+    virtual bool RecvAccumulateMixedContentHSTS(const URIParams& aURI, const bool& aActive) override;
+
     virtual bool DeallocPHalParent(PHalParent*) override;
 
     virtual PIccParent* AllocPIccParent(const uint32_t& aServiceId) override;
diff --git a/dom/ipc/PContent.ipdl b/dom/ipc/PContent.ipdl
index 8934cf05f88..a8dcf6ea2b8 100644
--- a/dom/ipc/PContent.ipdl
+++ b/dom/ipc/PContent.ipdl
@@ -751,6 +751,8 @@ parent:
     sync IsSecureURI(uint32_t type, URIParams uri, uint32_t flags)
         returns (bool isSecureURI);
 
+    async AccumulateMixedContentHSTS(URIParams uri, bool active);
+
     sync GetLookAndFeelCache()
         returns (LookAndFeelInt[] lookAndFeelIntCache);
 
@@ -788,7 +790,7 @@ parent:
     PFMRadio();
 
     PWebrtcGlobal();
-    
+
     PPresentation();
 
     // Services remoting
diff --git a/dom/ipc/moz.build b/dom/ipc/moz.build
index cf3981b490e..6bb479b9511 100644
--- a/dom/ipc/moz.build
+++ b/dom/ipc/moz.build
@@ -134,6 +134,7 @@ LOCAL_INCLUDES += [
     '/dom/geolocation',
     '/dom/media/webspeech/synth/ipc',
     '/dom/mobilemessage/ipc',
+    '/dom/security',
     '/dom/storage',
     '/dom/workers',
     '/editor/libeditor',
diff --git a/dom/security/moz.build b/dom/security/moz.build
index 8c99bd4366b..80890f46f29 100644
--- a/dom/security/moz.build
+++ b/dom/security/moz.build
@@ -33,6 +33,8 @@ UNIFIED_SOURCES += [
     'SRIMetadata.cpp',
 ]
 
+include('/ipc/chromium/chromium-config.mozbuild')
+
 FINAL_LIBRARY = 'xul'
 LOCAL_INCLUDES += [
     '/caps',
@@ -40,5 +42,5 @@ LOCAL_INCLUDES += [
 ]
 
 if CONFIG['GNU_CC']:
-    CFLAGS += ['-Wshadow', '-Wformat-security']
-    CXXFLAGS += ['-Wshadow', '-Wformat-security']
+    CFLAGS += ['-Wformat-security']
+    CXXFLAGS += ['-Wformat-security']
diff --git a/dom/security/nsMixedContentBlocker.cpp b/dom/security/nsMixedContentBlocker.cpp
index 5f6c47dddc9..59d8d662398 100644
--- a/dom/security/nsMixedContentBlocker.cpp
+++ b/dom/security/nsMixedContentBlocker.cpp
@@ -32,8 +32,13 @@
 #include "nsIChannelEventSink.h"
 #include "nsAsyncRedirectVerifyHelper.h"
 #include "mozilla/LoadInfo.h"
+#include "nsISiteSecurityService.h"
 
 #include "mozilla/Logging.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/ipc/URIUtils.h"
+
 
 using namespace mozilla;
 
@@ -342,7 +347,7 @@ nsMixedContentBlocker::ShouldLoad(uint32_t aContentType,
   // callers of this method don't know whether the load went through cached
   // image redirects.  This is handled by direct callers of the static
   // ShouldLoad.
-  nsresult rv = ShouldLoad(false,   //aHadInsecureImageRedirect
+  nsresult rv = ShouldLoad(false,   // aHadInsecureImageRedirect
                            aContentType,
                            aContentLocation,
                            aRequestingLocation,
@@ -381,7 +386,6 @@ nsMixedContentBlocker::ShouldLoad(bool aHadInsecureImageRedirect,
   // Make decision to block/reject by default
   *aDecision = REJECT_REQUEST;
 
-
   // Notes on non-obvious decisions:
   //
   // TYPE_DTD: A DTD can contain entity definitions that expand to scripts.
@@ -718,6 +722,33 @@ nsMixedContentBlocker::ShouldLoad(bool aHadInsecureImageRedirect,
   }
   nsresult stateRV = securityUI->GetState(&state);
 
+  // At this point we know that the request is mixed content, and the only
+  // question is whether we block it.  Record telemetry at this point as to
+  // whether HSTS would have fixed things by making the content location
+  // into an HTTPS URL.
+  //
+  // Note that we count this for redirects as well as primary requests. This
+  // will cause some degree of double-counting, especially when mixed content
+  // is not blocked (e.g., for images).  For more detail, see:
+  //   https://bugzilla.mozilla.org/show_bug.cgi?id=1198572#c19
+  //
+  // We do not count requests aHadInsecureImageRedirect=true, since these are
+  // just an artifact of the image caching system.
+  bool active = (classification == eMixedScript);
+  if (!aHadInsecureImageRedirect) {
+    if (XRE_IsParentProcess()) {
+      AccumulateMixedContentHSTS(aContentLocation, active);
+    } else {
+      // Ask the parent process to do the same call
+      mozilla::dom::ContentChild* cc = mozilla::dom::ContentChild::GetSingleton();
+      if (cc) {
+        mozilla::ipc::URIParams uri;
+        SerializeURI(aContentLocation, uri);
+        cc->SendAccumulateMixedContentHSTS(uri, active);
+      }
+    }
+  }
+
   // If the content is display content, and the pref says display content should be blocked, block it.
   if (sBlockMixedDisplay && classification == eMixedDisplay) {
     if (allowMixedContent) {
@@ -857,3 +888,54 @@ nsMixedContentBlocker::ShouldProcess(uint32_t aContentType,
                     aRequestingContext, aMimeGuess, aExtra, aRequestPrincipal,
                     aDecision);
 }
+
+enum MixedContentHSTSState {
+  MCB_HSTS_PASSIVE_NO_HSTS   = 0,
+  MCB_HSTS_PASSIVE_WITH_HSTS = 1,
+  MCB_HSTS_ACTIVE_NO_HSTS    = 2,
+  MCB_HSTS_ACTIVE_WITH_HSTS  = 3
+};
+
+// Record information on when HSTS would have made mixed content not mixed
+// content (regardless of whether it was actually blocked)
+void
+nsMixedContentBlocker::AccumulateMixedContentHSTS(nsIURI* aURI, bool aActive)
+{
+  // This method must only be called in the parent, because
+  // nsSiteSecurityService is only available in the parent
+  if (!XRE_IsParentProcess()) {
+    MOZ_ASSERT(false);
+    return;
+  }
+
+  bool hsts;
+  nsresult rv;
+  nsCOMPtr<nsISiteSecurityService> sss = do_GetService(NS_SSSERVICE_CONTRACTID, &rv);
+  if (NS_FAILED(rv)) {
+    return;
+  }
+  rv = sss->IsSecureURI(nsISiteSecurityService::HEADER_HSTS, aURI, 0, &hsts);
+  if (NS_FAILED(rv)) {
+    return;
+  }
+
+  if (!aActive) {
+    if (!hsts) {
+      Telemetry::Accumulate(Telemetry::MIXED_CONTENT_HSTS,
+                            MCB_HSTS_PASSIVE_NO_HSTS);
+    }
+    else {
+      Telemetry::Accumulate(Telemetry::MIXED_CONTENT_HSTS,
+                            MCB_HSTS_PASSIVE_WITH_HSTS);
+    }
+  } else {
+    if (!hsts) {
+      Telemetry::Accumulate(Telemetry::MIXED_CONTENT_HSTS,
+                            MCB_HSTS_ACTIVE_NO_HSTS);
+    }
+    else {
+      Telemetry::Accumulate(Telemetry::MIXED_CONTENT_HSTS,
+                            MCB_HSTS_ACTIVE_WITH_HSTS);
+    }
+  }
+}
diff --git a/dom/security/nsMixedContentBlocker.h b/dom/security/nsMixedContentBlocker.h
index e77189c2a6b..216466fd83b 100644
--- a/dom/security/nsMixedContentBlocker.h
+++ b/dom/security/nsMixedContentBlocker.h
@@ -59,6 +59,7 @@ public:
                              nsISupports* aExtra,
                              nsIPrincipal* aRequestPrincipal,
                              int16_t* aDecision);
+  static void AccumulateMixedContentHSTS(nsIURI* aURI, bool aActive);
   static bool sBlockMixedScript;
   static bool sBlockMixedDisplay;
 };
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index 1731e0eccf5..841bb2d18d7 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -7334,6 +7334,13 @@
     "n_values": 3,
     "description": "A simple counter of daily mixed-content unblock operations and top documents loaded"
   },
+  "MIXED_CONTENT_HSTS": {
+    "alert_emails": ["seceng@mozilla.org"],
+    "expires_in_version": "never",
+    "kind": "enumerated",
+    "n_values": 10,
+    "description": "How often would blocked mixed content be allowed if HSTS upgrades were allowed? 0=display/no-HSTS, 1=display/HSTS, 2=active/no-HSTS, 3=active/HSTS"
+  },
   "NTLM_MODULE_USED_2": {
     "expires_in_version": "never",
     "kind": "enumerated",