--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -2307,24 +2307,26 @@ ContentChild::RecvCycleCollect()
   }
   nsJSContext::CycleCollectNow();
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
 ContentChild::RecvAppInfo(const nsCString& version, const nsCString& buildID,
                           const nsCString& name, const nsCString& UAName,
-                          const nsCString& ID, const nsCString& vendor)
+                          const nsCString& ID, const nsCString& vendor,
+                          const bool& safeMode)
 {
   mAppInfo.version.Assign(version);
   mAppInfo.buildID.Assign(buildID);
   mAppInfo.name.Assign(name);
   mAppInfo.UAName.Assign(UAName);
   mAppInfo.ID.Assign(ID);
   mAppInfo.vendor.Assign(vendor);
+  mAppInfo.safeMode = safeMode;
 
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
 ContentChild::RecvRemoteType(const nsString& aRemoteType)
 {
   MOZ_ASSERT(DOMStringIsNull(mRemoteType));

--- a/dom/ipc/ContentChild.h
+++ b/dom/ipc/ContentChild.h
@@ -72,16 +72,17 @@ public:
   struct AppInfo
   {
     nsCString version;
     nsCString buildID;
     nsCString name;
     nsCString UAName;
     nsCString ID;
     nsCString vendor;
+    bool safeMode;
   };
 
   nsresult
   ProvideWindowCommon(TabChild* aTabOpener,
                       mozIDOMWindowProxy* aOpener,
                       bool aIframeMoz,
                       uint32_t aChromeFlags,
                       bool aCalledFromJS,
@@ -377,17 +378,18 @@ public:
   virtual mozilla::ipc::IPCResult RecvActivateA11y(const uint32_t& aMsaaID) override;
   virtual mozilla::ipc::IPCResult RecvShutdownA11y() override;
 
   virtual mozilla::ipc::IPCResult RecvGarbageCollect() override;
   virtual mozilla::ipc::IPCResult RecvCycleCollect() override;
 
   virtual mozilla::ipc::IPCResult RecvAppInfo(const nsCString& version, const nsCString& buildID,
                                               const nsCString& name, const nsCString& UAName,
-                                              const nsCString& ID, const nsCString& vendor) override;
+                                              const nsCString& ID, const nsCString& vendor,
+                                              const bool& safeMode) override;
 
   virtual mozilla::ipc::IPCResult RecvRemoteType(const nsString& aRemoteType) override;
 
   const nsAString& GetRemoteType() const;
 
   virtual mozilla::ipc::IPCResult
   RecvInitServiceWorkers(const ServiceWorkerConfiguration& aConfig) override;
 

--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -1911,17 +1911,17 @@ ContentParent::InitInternal(ProcessPrior
     nsCString version(gAppData->version);
     nsCString buildID(gAppData->buildID);
     nsCString name(gAppData->name);
     nsCString UAName(gAppData->UAName);
     nsCString ID(gAppData->ID);
     nsCString vendor(gAppData->vendor);
 
     // Sending all information to content process.
-    Unused << SendAppInfo(version, buildID, name, UAName, ID, vendor);
+    Unused << SendAppInfo(version, buildID, name, UAName, ID, vendor, gSafeMode);
   }
 
   // Initialize the message manager (and load delayed scripts) now that we
   // have established communications with the child.
   mMessageManager->InitWithCallback(this);
 
   // Send the child its remote type. On Mac, this needs to be sent prior
   // to the message we send to enable the Sandbox (SendStartProcessSandbox)

--- a/dom/ipc/PContent.ipdl
+++ b/dom/ipc/PContent.ipdl
@@ -505,17 +505,17 @@ child:
     async ActivateA11y(uint32_t aMsaaID);
 
     /**
      * Shutdown accessibility engine in content process (if not in use).
      */
     async ShutdownA11y();
 
     async AppInfo(nsCString version, nsCString buildID, nsCString name, nsCString UAName,
-                  nsCString ID, nsCString vendor);
+                  nsCString ID, nsCString vendor, bool safeMode);
 
     /**
      * Send the remote type associated with the content process.
      */
     async RemoteType(nsString aRemoteType);
 
     /**
      * Send ServiceWorkerRegistrationData to child process.

--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -804,16 +804,21 @@ nsXULAppInfo::SetLogConsoleErrors(bool a
 {
   gLogConsoleErrors = aValue;
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsXULAppInfo::GetInSafeMode(bool *aResult)
 {
+  if (XRE_IsContentProcess()) {
+    ContentChild* cc = ContentChild::GetSingleton();
+    *aResult = cc->GetAppInfo().safeMode;
+    return NS_OK;
+  }
   *aResult = gSafeMode;
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsXULAppInfo::GetOS(nsACString& aResult)
 {
   aResult.AssignLiteral(OS_TARGET);