diff --git a/content/base/public/nsIObjectLoadingContent.idl b/content/base/public/nsIObjectLoadingContent.idl
index 38a985802392..2c1466a30e9d 100644
--- a/content/base/public/nsIObjectLoadingContent.idl
+++ b/content/base/public/nsIObjectLoadingContent.idl
@@ -14,7 +14,7 @@ interface nsIDOMClientRect;
 interface nsIURI;
 
 %{C++
-#include "nsNPAPIPluginInstance.h"
+class nsNPAPIPluginInstance;
 %}
 [ptr] native nsNPAPIPluginInstancePtr(nsNPAPIPluginInstance);
 
diff --git a/content/base/src/nsContentUtils.cpp b/content/base/src/nsContentUtils.cpp
index 7a9067156fa7..17332a55fce5 100644
--- a/content/base/src/nsContentUtils.cpp
+++ b/content/base/src/nsContentUtils.cpp
@@ -120,6 +120,7 @@
 #include "nsINode.h"
 #include "nsINodeInfo.h"
 #include "nsIObjectLoadingContent.h"
+#include "nsNPAPIPluginInstance.h"
 #include "nsIObserver.h"
 #include "nsIObserverService.h"
 #include "nsIOfflineCacheUpdate.h"
diff --git a/content/base/src/nsObjectLoadingContent.cpp b/content/base/src/nsObjectLoadingContent.cpp
index 553b2a2fbace..ad042d2ee59c 100644
--- a/content/base/src/nsObjectLoadingContent.cpp
+++ b/content/base/src/nsObjectLoadingContent.cpp
@@ -25,6 +25,7 @@
 #include "nsIObjectFrame.h"
 #include "nsIPermissionManager.h"
 #include "nsPluginHost.h"
+#include "nsPluginInstanceOwner.h"
 #include "nsJSNPRuntime.h"
 #include "nsIPresShell.h"
 #include "nsIScriptGlobalObject.h"
diff --git a/content/base/src/nsObjectLoadingContent.h b/content/base/src/nsObjectLoadingContent.h
index d7f059cc5157..a5bacdc69762 100644
--- a/content/base/src/nsObjectLoadingContent.h
+++ b/content/base/src/nsObjectLoadingContent.h
@@ -19,7 +19,6 @@
 #include "nsIChannelEventSink.h"
 #include "nsIObjectLoadingContent.h"
 #include "nsIRunnable.h"
-#include "nsPluginInstanceOwner.h"
 #include "nsIThreadInternal.h"
 #include "nsIFrame.h"
 #include "nsIFrameLoader.h"
@@ -30,6 +29,7 @@ class AutoSetInstantiatingToFalse;
 class nsObjectFrame;
 class nsFrameLoader;
 class nsXULElement;
+class nsPluginInstanceOwner;
 
 class nsObjectLoadingContent : public nsImageLoadingContent
                              , public nsIStreamListener
diff --git a/dom/base/nsPluginArray.h b/dom/base/nsPluginArray.h
index 4100278c9519..8635b2b7318d 100644
--- a/dom/base/nsPluginArray.h
+++ b/dom/base/nsPluginArray.h
@@ -12,8 +12,8 @@
 #include "nsIObserver.h"
 #include "nsWrapperCache.h"
 #include "nsPluginTags.h"
+#include "nsPIDOMWindow.h"
 
-class nsPIDOMWindow;
 class nsPluginElement;
 class nsMimeType;
 
diff --git a/dom/plugins/base/PluginPRLibrary.cpp b/dom/plugins/base/PluginPRLibrary.cpp
index a50898d29781..a2afaec5d5e4 100644
--- a/dom/plugins/base/PluginPRLibrary.cpp
+++ b/dom/plugins/base/PluginPRLibrary.cpp
@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/PluginPRLibrary.h"
+#include "nsNPAPIPluginInstance.h"
 
 // Some plugins on Windows, notably Quake Live, implement NP_Initialize using
 // cdecl instead of the documented stdcall. In order to work around this,
diff --git a/dom/plugins/base/nsIPluginInstanceOwner.idl b/dom/plugins/base/nsIPluginInstanceOwner.idl
index 5a7930eaf27e..58e109cd47fe 100644
--- a/dom/plugins/base/nsIPluginInstanceOwner.idl
+++ b/dom/plugins/base/nsIPluginInstanceOwner.idl
@@ -11,7 +11,7 @@ interface nsIDocument;
 
 %{C++
 #include "npapi.h"
-#include "nsNPAPIPluginInstance.h"
+class nsNPAPIPluginInstance;
 class nsPluginEvent;
 %}
 
diff --git a/dom/plugins/base/nsNPAPIPluginStreamListener.h b/dom/plugins/base/nsNPAPIPluginStreamListener.h
index 3099109eda65..b851b3794f5c 100644
--- a/dom/plugins/base/nsNPAPIPluginStreamListener.h
+++ b/dom/plugins/base/nsNPAPIPluginStreamListener.h
@@ -15,7 +15,6 @@
 #include "nsIOutputStream.h"
 #include "nsIPluginInstanceOwner.h"
 #include "nsString.h"
-#include "nsNPAPIPluginInstance.h"
 #include "nsIAsyncVerifyRedirectCallback.h"
 #include "mozilla/PluginLibrary.h"
 
@@ -23,6 +22,8 @@
 
 class nsPluginStreamListenerPeer;
 class nsNPAPIPluginStreamListener;
+class nsNPAPIPluginInstance;
+class nsIChannel;
 
 class nsNPAPIStreamWrapper
 {
diff --git a/dom/plugins/base/nsPluginHost.cpp b/dom/plugins/base/nsPluginHost.cpp
index eaaa855c8f42..92e238fffb3c 100644
--- a/dom/plugins/base/nsPluginHost.cpp
+++ b/dom/plugins/base/nsPluginHost.cpp
@@ -3651,6 +3651,18 @@ PRCList nsPluginDestroyRunnable::sRunnableListHead =
 PRCList PluginDestructionGuard::sListHead =
   PR_INIT_STATIC_CLIST(&PluginDestructionGuard::sListHead);
 
+PluginDestructionGuard::PluginDestructionGuard(nsNPAPIPluginInstance *aInstance)
+  : mInstance(aInstance)
+{
+  Init();
+}
+
+PluginDestructionGuard::PluginDestructionGuard(NPP npp)
+  : mInstance(npp ? static_cast<nsNPAPIPluginInstance*>(npp->ndata) : nullptr)
+{
+  Init();
+}
+
 PluginDestructionGuard::~PluginDestructionGuard()
 {
   NS_ASSERTION(NS_IsMainThread(), "Should be on the main thread");
diff --git a/dom/plugins/base/nsPluginHost.h b/dom/plugins/base/nsPluginHost.h
index 1c0d0bc39bb2..06b576a8b00a 100644
--- a/dom/plugins/base/nsPluginHost.h
+++ b/dom/plugins/base/nsPluginHost.h
@@ -12,7 +12,6 @@
 #include "prlink.h"
 #include "prclist.h"
 #include "npapi.h"
-#include "nsNPAPIPluginInstance.h"
 #include "nsIPluginTag.h"
 #include "nsPluginsDir.h"
 #include "nsPluginDirServiceProvider.h"
@@ -37,6 +36,11 @@ class nsIChannel;
 class nsPluginNativeWindow;
 class nsObjectLoadingContent;
 class nsPluginInstanceOwner;
+class nsNPAPIPluginInstance;
+class nsNPAPIPluginStreamListener;
+class nsIPluginInstanceOwner;
+class nsIInputStream;
+class nsIStreamListener;
 
 class nsInvalidPluginTag : public nsISupports
 {
@@ -303,17 +307,9 @@ private:
 class MOZ_STACK_CLASS PluginDestructionGuard : protected PRCList
 {
 public:
-  PluginDestructionGuard(nsNPAPIPluginInstance *aInstance)
-    : mInstance(aInstance)
-  {
-    Init();
-  }
+  PluginDestructionGuard(nsNPAPIPluginInstance *aInstance);
 
-  PluginDestructionGuard(NPP npp)
-    : mInstance(npp ? static_cast<nsNPAPIPluginInstance*>(npp->ndata) : nullptr)
-  {
-    Init();
-  }
+  PluginDestructionGuard(NPP npp);
 
   ~PluginDestructionGuard();
 
diff --git a/dom/plugins/base/nsPluginTags.h b/dom/plugins/base/nsPluginTags.h
index 5451fe3e733f..c166ac3b9c0b 100644
--- a/dom/plugins/base/nsPluginTags.h
+++ b/dom/plugins/base/nsPluginTags.h
@@ -12,12 +12,13 @@
 #include "nsCOMPtr.h"
 #include "nsCOMArray.h"
 #include "nsIPluginTag.h"
-#include "nsNPAPIPluginInstance.h"
 #include "nsITimer.h"
+#include "nsStringGlue.h"
 
 class nsPluginHost;
 struct PRLibrary;
 struct nsPluginInfo;
+class nsNPAPIPlugin;
 
 // A linked-list of plugin information that is used for instantiating plugins
 // and reflecting plugin information into JavaScript.
diff --git a/dom/plugins/ipc/PluginInstanceParent.cpp b/dom/plugins/ipc/PluginInstanceParent.cpp
index 7b87869ac5d8..4793c113d081 100644
--- a/dom/plugins/ipc/PluginInstanceParent.cpp
+++ b/dom/plugins/ipc/PluginInstanceParent.cpp
@@ -26,7 +26,6 @@
 #include "gfxContext.h"
 #include "gfxColor.h"
 #include "gfxUtils.h"
-#include "nsNPAPIPluginInstance.h"
 #include "Layers.h"
 #include "SharedTextureImage.h"
 #include "GLContext.h"