--- a/dom/events/IMEStateManager.cpp
+++ b/dom/events/IMEStateManager.cpp
@@ -342,17 +342,17 @@ IMEStateManager::OnDestroyPresContext(ns
   DestroyIMEContentObserver();
 
   if (sWidget) {
     IMEState newState = GetNewIMEState(sPresContext, nullptr);
     InputContextAction action(InputContextAction::CAUSE_UNKNOWN,
                               InputContextAction::LOST_FOCUS);
     InputContext::Origin origin =
       sActiveTabParent ? InputContext::ORIGIN_CONTENT : sOrigin;
-    SetIMEState(newState, nullptr, sWidget, action, origin);
+    SetIMEState(newState, nullptr, nullptr, sWidget, action, origin);
   }
   sWidget = nullptr;
   sContent = nullptr;
   sPresContext = nullptr;
   sActiveTabParent = nullptr;
   return NS_OK;
 }
 
@@ -399,17 +399,17 @@ IMEStateManager::OnRemoveContent(nsPresC
 
   // Current IME transaction should commit
   if (sWidget) {
     IMEState newState = GetNewIMEState(sPresContext, nullptr);
     InputContextAction action(InputContextAction::CAUSE_UNKNOWN,
                               InputContextAction::LOST_FOCUS);
     InputContext::Origin origin =
       sActiveTabParent ? InputContext::ORIGIN_CONTENT : sOrigin;
-    SetIMEState(newState, nullptr, sWidget, action, origin);
+    SetIMEState(newState, aPresContext, nullptr, sWidget, action, origin);
   }
 
   sWidget = nullptr;
   sContent = nullptr;
   sPresContext = nullptr;
   sActiveTabParent = nullptr;
 
   return NS_OK;
@@ -629,17 +629,17 @@ IMEStateManager::OnChangeFocusInternal(n
       // focus.
       bool gotFocus = aContent || (newState.mEnabled == IMEState::ENABLED);
       aAction.mFocusChange =
         gotFocus ? InputContextAction::GOT_FOCUS :
                    InputContextAction::LOST_FOCUS;
     }
 
     // Update IME state for new focus widget
-    SetIMEState(newState, aContent, newWidget, aAction,
+    SetIMEState(newState, aPresContext, aContent, newWidget, aAction,
                 newTabParent ? InputContext::ORIGIN_CONTENT : sOrigin);
   }
 
   sActiveTabParent = newTabParent;
   sPresContext = aPresContext;
   sContent = aContent;
 
   // Don't call CreateIMEContentObserver() here except when a plugin gets
@@ -781,17 +781,17 @@ IMEStateManager::OnClickInEditor(nsPresC
   }
 
   InputContextAction::Cause cause =
     aMouseEvent->inputSource == nsIDOMMouseEvent::MOZ_SOURCE_TOUCH ?
       InputContextAction::CAUSE_TOUCH : InputContextAction::CAUSE_MOUSE;
 
   InputContextAction action(cause, InputContextAction::FOCUS_NOT_CHANGED);
   IMEState newState = GetNewIMEState(aPresContext, aContent);
-  SetIMEState(newState, aContent, widget, action, sOrigin);
+  SetIMEState(newState, aPresContext, aContent, widget, action, sOrigin);
 }
 
 // static
 void
 IMEStateManager::OnFocusInEditor(nsPresContext* aPresContext,
                                  nsIContent* aContent,
                                  EditorBase& aEditorBase)
 {
@@ -990,17 +990,17 @@ IMEStateManager::UpdateIMEState(const IM
 
   if (createTextStateManager) {
     DestroyIMEContentObserver();
   }
 
   if (updateIMEState) {
     InputContextAction action(InputContextAction::CAUSE_UNKNOWN,
                               InputContextAction::FOCUS_NOT_CHANGED);
-    SetIMEState(aNewIMEState, aContent, widget, action, sOrigin);
+    SetIMEState(aNewIMEState, presContext, aContent, widget, action, sOrigin);
     if (NS_WARN_IF(widget->Destroyed())) {
       MOZ_LOG(sISMLog, LogLevel::Error,
         ("  UpdateIMEState(), widget has gone during setting input context"));
       return;
     }
   }
 
   if (createTextStateManager) {
@@ -1100,25 +1100,26 @@ void
 IMEStateManager::SetInputContextForChildProcess(
                    TabParent* aTabParent,
                    const InputContext& aInputContext,
                    const InputContextAction& aAction)
 {
   MOZ_LOG(sISMLog, LogLevel::Info,
     ("SetInputContextForChildProcess(aTabParent=0x%p, "
      "aInputContext={ mIMEState={ mEnabled=%s, mOpen=%s }, "
-     "mHTMLInputType=\"%s\", mHTMLInputInputmode=\"%s\", mActionHint=\"%s\" }, "
-     "aAction={ mCause=%s, mAction=%s }), "
+     "mHTMLInputType=\"%s\", mHTMLInputInputmode=\"%s\", mActionHint=\"%s\", "
+     "mInPrivateBrowsing=%s }, aAction={ mCause=%s, mAction=%s }), "
      "sPresContext=0x%p (available: %s), sWidget=0x%p (available: %s), "
      "sActiveTabParent=0x%p",
      aTabParent, GetIMEStateEnabledName(aInputContext.mIMEState.mEnabled),
      GetIMEStateSetOpenName(aInputContext.mIMEState.mOpen),
      NS_ConvertUTF16toUTF8(aInputContext.mHTMLInputType).get(),
      NS_ConvertUTF16toUTF8(aInputContext.mHTMLInputInputmode).get(),
      NS_ConvertUTF16toUTF8(aInputContext.mActionHint).get(),
+     GetBoolName(aInputContext.mInPrivateBrowsing),
      GetActionCauseName(aAction.mCause),
      GetActionFocusChangeName(aAction.mFocusChange),
      sPresContext.get(), GetBoolName(CanHandleWith(sPresContext)),
      sWidget, GetBoolName(sWidget && !sWidget->Destroyed()),
      sActiveTabParent.get()));
 
   if (aTabParent != sActiveTabParent) {
     MOZ_LOG(sISMLog, LogLevel::Error,
@@ -1148,16 +1149,17 @@ IMEStateManager::SetInputContextForChild
   MOZ_ASSERT(aInputContext.mOrigin == InputContext::ORIGIN_CONTENT);
 
   SetInputContext(widget, aInputContext, aAction);
 }
 
 // static
 void
 IMEStateManager::SetIMEState(const IMEState& aState,
+                             nsPresContext* aPresContext,
                              nsIContent* aContent,
                              nsIWidget* aWidget,
                              InputContextAction aAction,
                              InputContext::Origin aOrigin)
 {
   MOZ_LOG(sISMLog, LogLevel::Info,
     ("SetIMEState(aState={ mEnabled=%s, mOpen=%s }, "
      "aContent=0x%p (TabParent=0x%p), aWidget=0x%p, aAction={ mCause=%s, "
@@ -1172,16 +1174,20 @@ IMEStateManager::SetIMEState(const IMESt
   NS_ENSURE_TRUE_VOID(aWidget);
 
   InputContext context;
   context.mIMEState = aState;
   context.mOrigin = aOrigin;
   context.mMayBeIMEUnaware = context.mIMEState.IsEditable() &&
     sCheckForIMEUnawareWebApps && MayBeIMEUnawareWebApp(aContent);
 
+  context.mInPrivateBrowsing =
+    aPresContext &&
+    nsContentUtils::IsInPrivateBrowsing(aPresContext->Document());
+
   if (aContent &&
       aContent->IsAnyOfHTMLElements(nsGkAtoms::input, nsGkAtoms::textarea)) {
     if (!aContent->IsHTMLElement(nsGkAtoms::textarea)) {
       // <input type=number> has an anonymous <input type=text> descendant
       // that gets focus whenever anyone tries to focus the number control. We
       // need to check if aContent is one of those anonymous text controls and,
       // if so, use the number control instead:
       nsIContent* content = aContent;
@@ -1256,24 +1262,26 @@ IMEStateManager::SetIMEState(const IMESt
 void
 IMEStateManager::SetInputContext(nsIWidget* aWidget,
                                  const InputContext& aInputContext,
                                  const InputContextAction& aAction)
 {
   MOZ_LOG(sISMLog, LogLevel::Info,
     ("SetInputContext(aWidget=0x%p, aInputContext={ "
      "mIMEState={ mEnabled=%s, mOpen=%s }, mHTMLInputType=\"%s\", "
-     "mHTMLInputInputmode=\"%s\", mActionHint=\"%s\" }, "
+     "mHTMLInputInputmode=\"%s\", mActionHint=\"%s\", "
+     "mInPrivateBrowsing=%s }, "
      "aAction={ mCause=%s, mAction=%s }), sActiveTabParent=0x%p",
      aWidget,
      GetIMEStateEnabledName(aInputContext.mIMEState.mEnabled),
      GetIMEStateSetOpenName(aInputContext.mIMEState.mOpen),
      NS_ConvertUTF16toUTF8(aInputContext.mHTMLInputType).get(),
      NS_ConvertUTF16toUTF8(aInputContext.mHTMLInputInputmode).get(),
      NS_ConvertUTF16toUTF8(aInputContext.mActionHint).get(),
+     GetBoolName(aInputContext.mInPrivateBrowsing),
      GetActionCauseName(aAction.mCause),
      GetActionFocusChangeName(aAction.mFocusChange),
      sActiveTabParent.get()));
 
   MOZ_RELEASE_ASSERT(aWidget);
 
   nsCOMPtr<nsIWidget> widget(aWidget);
   widget->SetInputContext(aInputContext, aAction);

--- a/dom/events/IMEStateManager.h
+++ b/dom/events/IMEStateManager.h
@@ -255,16 +255,17 @@ public:
    */
   static IMEContentObserver* GetActiveContentObserver();
 
 protected:
   static nsresult OnChangeFocusInternal(nsPresContext* aPresContext,
                                         nsIContent* aContent,
                                         InputContextAction aAction);
   static void SetIMEState(const IMEState &aState,
+                          nsPresContext* aPresContext,
                           nsIContent* aContent,
                           nsIWidget* aWidget,
                           InputContextAction aAction,
                           InputContext::Origin aOrigin);
   static void SetInputContext(nsIWidget* aWidget,
                               const InputContext& aInputContext,
                               const InputContextAction& aAction);
   static IMEState GetNewIMEState(nsPresContext* aPresContext,

--- a/dom/ipc/PBrowser.ipdl
+++ b/dom/ipc/PBrowser.ipdl
@@ -349,16 +349,17 @@ parent:
     nested(inside_cpow) sync GetInputContext() returns (int32_t IMEEnabled,
                                                         int32_t IMEOpen);
 
     nested(inside_cpow) async SetInputContext(int32_t IMEEnabled,
                                               int32_t IMEOpen,
                                               nsString type,
                                               nsString inputmode,
                                               nsString actionHint,
+                                              bool inPrivateBrowsing,
                                               int32_t cause,
                                               int32_t focusChange);
 
     sync IsParentWindowMainWidgetVisible() returns (bool visible);
 
     /**
      * Set the native cursor.
      * @param value

--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -2330,26 +2330,28 @@ TabParent::RecvGetInputContext(int32_t* 
 }
 
 mozilla::ipc::IPCResult
 TabParent::RecvSetInputContext(const int32_t& aIMEEnabled,
                                const int32_t& aIMEOpen,
                                const nsString& aType,
                                const nsString& aInputmode,
                                const nsString& aActionHint,
+                               const bool& aInPrivateBrowsing,
                                const int32_t& aCause,
                                const int32_t& aFocusChange)
 {
   InputContext context;
   context.mIMEState.mEnabled = static_cast<IMEState::Enabled>(aIMEEnabled);
   context.mIMEState.mOpen = static_cast<IMEState::Open>(aIMEOpen);
   context.mHTMLInputType.Assign(aType);
   context.mHTMLInputInputmode.Assign(aInputmode);
   context.mActionHint.Assign(aActionHint);
   context.mOrigin = InputContext::ORIGIN_CONTENT;
+  context.mInPrivateBrowsing = aInPrivateBrowsing;
 
   InputContextAction action(
     static_cast<InputContextAction::Cause>(aCause),
     static_cast<InputContextAction::FocusChange>(aFocusChange));
 
   IMEStateManager::SetInputContextForChildProcess(this, context, action);
 
   return IPC_OK();

--- a/dom/ipc/TabParent.h
+++ b/dom/ipc/TabParent.h
@@ -245,16 +245,17 @@ public:
   virtual mozilla::ipc::IPCResult RecvGetInputContext(int32_t* aIMEEnabled,
                                                       int32_t* aIMEOpen) override;
 
   virtual mozilla::ipc::IPCResult RecvSetInputContext(const int32_t& aIMEEnabled,
                                                       const int32_t& aIMEOpen,
                                                       const nsString& aType,
                                                       const nsString& aInputmode,
                                                       const nsString& aActionHint,
+                                                      const bool& aInPrivateBrowsing,
                                                       const int32_t& aCause,
                                                       const int32_t& aFocusChange) override;
 
 
   // See nsIKeyEventInPluginCallback
   virtual void HandledWindowedPluginKeyEvent(
                  const NativeEventData& aKeyEventData,
                  bool aIsConsumed) override;

--- a/widget/IMEData.h
+++ b/widget/IMEData.h
@@ -266,16 +266,17 @@ struct NativeIMEContext final
   }
 };
 
 struct InputContext final
 {
   InputContext()
     : mOrigin(XRE_IsParentProcess() ? ORIGIN_MAIN : ORIGIN_CONTENT)
     , mMayBeIMEUnaware(false)
+    , mInPrivateBrowsing(false)
   {
   }
 
   bool IsPasswordEditor() const
   {
     return mHTMLInputType.LowerCaseEqualsLiteral("password");
   }
 
@@ -303,16 +304,20 @@ struct InputContext final
   };
   Origin mOrigin;
 
   /* True if the webapp may be unaware of IME events such as input event or
    * composiion events. This enables a key-events-only mode on Android for
    * compatibility with webapps relying on key listeners. */
   bool mMayBeIMEUnaware;
 
+  /* Whether the owning document of the input element has been loaded
+   * in private browsing mode. */
+  bool mInPrivateBrowsing;
+
   bool IsOriginMainProcess() const
   {
     return mOrigin == ORIGIN_MAIN;
   }
 
   bool IsOriginContentProcess() const
   {
     return mOrigin == ORIGIN_CONTENT;

--- a/widget/PuppetWidget.cpp
+++ b/widget/PuppetWidget.cpp
@@ -733,16 +733,17 @@ PuppetWidget::SetInputContext(const Inpu
     return;
   }
   mTabChild->SendSetInputContext(
     static_cast<int32_t>(aContext.mIMEState.mEnabled),
     static_cast<int32_t>(aContext.mIMEState.mOpen),
     aContext.mHTMLInputType,
     aContext.mHTMLInputInputmode,
     aContext.mActionHint,
+    aContext.mInPrivateBrowsing,
     static_cast<int32_t>(aAction.mCause),
     static_cast<int32_t>(aAction.mFocusChange));
 }
 
 InputContext
 PuppetWidget::GetInputContext()
 {
   // XXX Currently, we don't support retrieving IME open state from child