diff --git a/content/base/public/nsDeprecatedOperationList.h b/content/base/public/nsDeprecatedOperationList.h
index ff72fddd538..27c42a03472 100644
--- a/content/base/public/nsDeprecatedOperationList.h
+++ b/content/base/public/nsDeprecatedOperationList.h
@@ -1,6 +1,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsIDocument.h"
 
 /*
  * This file contains the list of deprecated DOM operations.  It is
diff --git a/content/base/src/nsGkAtomList.h b/content/base/src/nsGkAtomList.h
index 14dd5bb5cdd..4f8f55e7ff7 100644
--- a/content/base/src/nsGkAtomList.h
+++ b/content/base/src/nsGkAtomList.h
@@ -2,7 +2,6 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
 // IWYU pragma: private, include "nsGkAtoms.h"
 
 /*
diff --git a/content/events/public/nsVKList.h b/content/events/public/nsVKList.h
index 063de995f98..79dd880fd9b 100644
--- a/content/events/public/nsVKList.h
+++ b/content/events/public/nsVKList.h
@@ -3,6 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsGUIEvent.h"
 
 /**
  * This header file defines all DOM keys which are defined in nsIDOMKeyEvent.
diff --git a/content/html/content/src/HTMLBodyElement.cpp b/content/html/content/src/HTMLBodyElement.cpp
index 7e4ee379660..07591628dfd 100644
--- a/content/html/content/src/HTMLBodyElement.cpp
+++ b/content/html/content/src/HTMLBodyElement.cpp
@@ -541,7 +541,7 @@ HTMLBodyElement::IsEventAttributeName(nsIAtom *aName)
   WINDOW_EVENT_HELPER(name_, EventHandlerNonNull)
 #define BEFOREUNLOAD_EVENT(name_, id_, type_, struct_)                         \
   WINDOW_EVENT_HELPER(name_, BeforeUnloadEventHandlerNonNull)
-#include "nsEventNameList.h"
+#include "nsEventNameList.h" // IWYU pragma: keep
 #undef BEFOREUNLOAD_EVENT
 #undef WINDOW_EVENT
 #undef WINDOW_EVENT_HELPER
diff --git a/content/html/content/src/HTMLBodyElement.h b/content/html/content/src/HTMLBodyElement.h
index 5db7abfd091..6bd61d026e6 100644
--- a/content/html/content/src/HTMLBodyElement.h
+++ b/content/html/content/src/HTMLBodyElement.h
@@ -65,7 +65,7 @@ public:
   WINDOW_EVENT_HELPER(name_, EventHandlerNonNull)
 #define BEFOREUNLOAD_EVENT(name_, id_, type_, struct_)                  \
   WINDOW_EVENT_HELPER(name_, BeforeUnloadEventHandlerNonNull)
-#include "nsEventNameList.h"
+#include "nsEventNameList.h" // IWYU pragma: keep
 #undef BEFOREUNLOAD_EVENT
 #undef WINDOW_EVENT
 #undef WINDOW_EVENT_HELPER
diff --git a/content/html/content/src/HTMLFrameSetElement.cpp b/content/html/content/src/HTMLFrameSetElement.cpp
index ca05b634250..2f0bdf5c2ff 100644
--- a/content/html/content/src/HTMLFrameSetElement.cpp
+++ b/content/html/content/src/HTMLFrameSetElement.cpp
@@ -400,7 +400,7 @@ HTMLFrameSetElement::IsEventAttributeName(nsIAtom *aName)
   WINDOW_EVENT_HELPER(name_, EventHandlerNonNull)
 #define BEFOREUNLOAD_EVENT(name_, id_, type_, struct_)                         \
   WINDOW_EVENT_HELPER(name_, BeforeUnloadEventHandlerNonNull)
-#include "nsEventNameList.h"
+#include "nsEventNameList.h" // IWYU pragma: keep
 #undef BEFOREUNLOAD_EVENT
 #undef WINDOW_EVENT
 #undef WINDOW_EVENT_HELPER
diff --git a/content/html/content/src/HTMLFrameSetElement.h b/content/html/content/src/HTMLFrameSetElement.h
index c1fe9c77d32..541dea6ba63 100644
--- a/content/html/content/src/HTMLFrameSetElement.h
+++ b/content/html/content/src/HTMLFrameSetElement.h
@@ -95,7 +95,7 @@ public:
   WINDOW_EVENT_HELPER(name_, EventHandlerNonNull)
 #define BEFOREUNLOAD_EVENT(name_, id_, type_, struct_)                  \
   WINDOW_EVENT_HELPER(name_, BeforeUnloadEventHandlerNonNull)
-#include "nsEventNameList.h"
+#include "nsEventNameList.h" // IWYU pragma: keep
 #undef BEFOREUNLOAD_EVENT
 #undef WINDOW_EVENT
 #undef WINDOW_EVENT_HELPER
diff --git a/content/html/content/src/nsGenericHTMLElement.cpp b/content/html/content/src/nsGenericHTMLElement.cpp
index b96f979a531..eb9c6dd30e4 100644
--- a/content/html/content/src/nsGenericHTMLElement.cpp
+++ b/content/html/content/src/nsGenericHTMLElement.cpp
@@ -820,7 +820,7 @@ nsGenericHTMLElement::GetEventListenerManagerForAttr(nsIAtom* aAttrName,
 #define FORWARDED_EVENT(name_, id_, type_, struct_) \
        || nsGkAtoms::on##name_ == aAttrName
 #define WINDOW_EVENT FORWARDED_EVENT
-#include "nsEventNameList.h"
+#include "nsEventNameList.h" // IWYU pragma: keep
 #undef WINDOW_EVENT
 #undef FORWARDED_EVENT
 #undef EVENT
@@ -928,7 +928,7 @@ nsGenericHTMLElement::SetOn##name_(EventHandlerNonNull* handler,              \
                                                                               \
   return nsINode::SetOn##name_(handler, error);                               \
 }
-#include "nsEventNameList.h"
+#include "nsEventNameList.h" // IWYU pragma: keep
 #undef ERROR_EVENT
 #undef FORWARDED_EVENT
 #undef EVENT
diff --git a/content/html/content/src/nsGenericHTMLElement.h b/content/html/content/src/nsGenericHTMLElement.h
index da80bb593d5..56da1a3ad55 100644
--- a/content/html/content/src/nsGenericHTMLElement.h
+++ b/content/html/content/src/nsGenericHTMLElement.h
@@ -247,7 +247,7 @@ public:
   already_AddRefed<mozilla::dom::EventHandlerNonNull> GetOn##name_();         \
   void SetOn##name_(mozilla::dom::EventHandlerNonNull* handler,               \
                     mozilla::ErrorResult& error);
-#include "nsEventNameList.h"
+#include "nsEventNameList.h" // IWYU pragma: keep
 #undef ERROR_EVENT
 #undef FORWARDED_EVENT
 #undef EVENT
diff --git a/dom/base/nsDOMClassInfoClasses.h b/dom/base/nsDOMClassInfoClasses.h
index 1d6cd8d7d40..128cc96b051 100644
--- a/dom/base/nsDOMClassInfoClasses.h
+++ b/dom/base/nsDOMClassInfoClasses.h
@@ -2,6 +2,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsDOMClassInfoID.h"
 
 DOMCI_CLASS(Window)
 DOMCI_CLASS(Location)
diff --git a/tools/profiler/GeckoProfilerImpl.h b/tools/profiler/GeckoProfilerImpl.h
index 02e53ba8b49..d147c2cc058 100644
--- a/tools/profiler/GeckoProfilerImpl.h
+++ b/tools/profiler/GeckoProfilerImpl.h
@@ -2,6 +2,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "GeckoProfiler.h"
 
 #ifndef TOOLS_SPS_SAMPLER_H_
 #define TOOLS_SPS_SAMPLER_H_
diff --git a/xpcom/base/ErrorList.h b/xpcom/base/ErrorList.h
index 904686dbb47..daf959d4af5 100644
--- a/xpcom/base/ErrorList.h
+++ b/xpcom/base/ErrorList.h
@@ -1,3 +1,4 @@
+// IWYU pragma: private, include "nsError.h"
 /* Helper file for nsError.h, via preprocessor magic */
   /* Standard "it worked" return value */
   ERROR(NS_OK,  0),
diff --git a/xpcom/base/Makefile.in b/xpcom/base/Makefile.in
index 4f1f39b7bd3..de07083a71c 100644
--- a/xpcom/base/Makefile.in
+++ b/xpcom/base/Makefile.in
@@ -43,7 +43,8 @@ LOCAL_INCLUDES += \
 # suppresses printing the pattern space, and the p at the end prints it anyway,
 # so we don't print lines that don't match the pattern to start with.
 ErrorListCxxDefines.h: ErrorList.h Makefile
-		sed -n 's/.*ERROR(\([A-Z_0-9]*\).*/#define \1 nsresult::\1/p' < $< > $@
+	echo '// IWYU pragma: private, include "nsError.h"' > $@
+	sed -n 's/.*ERROR(\([A-Z_0-9]*\).*/#define \1 nsresult::\1/p' < $< >> $@
 
 ErrorListCDefines.h: ErrorList.h Makefile
 		sed 's/.*ERROR(\([A-Z_0-9]*\),\( *\)\(.*\))[^)]*/#define \1 \2((nsresult)(\3))/' < $< > $@
diff --git a/xpcom/base/nsISupportsBase.h b/xpcom/base/nsISupportsBase.h
index e3b7419757e..d2f66f4a68f 100644
--- a/xpcom/base/nsISupportsBase.h
+++ b/xpcom/base/nsISupportsBase.h
@@ -1,6 +1,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsISupports.h"
 
 #ifndef nsISupportsBase_h__
 #define nsISupportsBase_h__
diff --git a/xpcom/build/ServiceList.h b/xpcom/build/ServiceList.h
index 2630948e1d8..78a9c5aa311 100644
--- a/xpcom/build/ServiceList.h
+++ b/xpcom/build/ServiceList.h
@@ -1,7 +1,6 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
 // IWYU pragma: private, include "mozilla/Services.h"
 
 #ifdef ACCESSIBILITY
diff --git a/xpcom/glue/nsISupportsImpl.h b/xpcom/glue/nsISupportsImpl.h
index d5f08ff5667..ffd9a057081 100644
--- a/xpcom/glue/nsISupportsImpl.h
+++ b/xpcom/glue/nsISupportsImpl.h
@@ -2,6 +2,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsISupports.h"
 
 
 #ifndef nsISupportsImpl_h__
diff --git a/xpcom/string/public/nsAString.h b/xpcom/string/public/nsAString.h
index 688ab1fa980..506d7bb1c23 100644
--- a/xpcom/string/public/nsAString.h
+++ b/xpcom/string/public/nsAString.h
@@ -3,6 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsStringGlue.h"
 
 #ifndef nsAString_h___
 #define nsAString_h___
diff --git a/xpcom/string/public/nsReadableUtils.h b/xpcom/string/public/nsReadableUtils.h
index 72e439ad18b..a222d8cc28d 100644
--- a/xpcom/string/public/nsReadableUtils.h
+++ b/xpcom/string/public/nsReadableUtils.h
@@ -2,6 +2,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsStringGlue.h"
 
 #ifndef nsReadableUtils_h___
 #define nsReadableUtils_h___
diff --git a/xpcom/string/public/nsString.h b/xpcom/string/public/nsString.h
index 39d83cd5dce..3f55072cb15 100644
--- a/xpcom/string/public/nsString.h
+++ b/xpcom/string/public/nsString.h
@@ -3,6 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsStringGlue.h"
 
 #ifndef nsString_h___
 #define nsString_h___
diff --git a/xpcom/string/public/nsTDependentSubstring.h b/xpcom/string/public/nsTDependentSubstring.h
index 88538e610d2..61c84c2f2d7 100644
--- a/xpcom/string/public/nsTDependentSubstring.h
+++ b/xpcom/string/public/nsTDependentSubstring.h
@@ -3,8 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-// IWYU pragma: private, include "nsDependentSubstring.h"
+// IWYU pragma: private, include "nsStringGlue.h"
 
   /**
    * nsTDependentSubstring_CharT
diff --git a/xpcom/string/public/nsTString.h b/xpcom/string/public/nsTString.h
index 0af5a5bd48d..be633bd56e2 100644
--- a/xpcom/string/public/nsTString.h
+++ b/xpcom/string/public/nsTString.h
@@ -3,8 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-// IWYU pragma: private, include "nsString.h"
+// IWYU pragma: private, include "nsStringGlue.h"
 
   /**
    * This is the canonical null-terminated string class.  All subclasses
diff --git a/xpcom/string/public/nsTSubstring.h b/xpcom/string/public/nsTSubstring.h
index f73ce8b20b5..fa7099fd6f3 100644
--- a/xpcom/string/public/nsTSubstring.h
+++ b/xpcom/string/public/nsTSubstring.h
@@ -3,8 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-// IWYU pragma: private, include "nsAString.h"
+// IWYU pragma: private, include "nsStringGlue.h"
 
 #include "mozilla/MemoryReporting.h"
 
diff --git a/xpcom/string/public/nsTSubstringTuple.h b/xpcom/string/public/nsTSubstringTuple.h
index f96a45e713b..103d292528a 100644
--- a/xpcom/string/public/nsTSubstringTuple.h
+++ b/xpcom/string/public/nsTSubstringTuple.h
@@ -3,8 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-// IWYU pragma: private, include "nsSubstringTuple.h"
+// IWYU pragma: private, include "nsStringGlue.h"
 
   /**
    * nsTSubstringTuple_CharT
diff --git a/xpcom/string/public/string-template-def-char.h b/xpcom/string/public/string-template-def-char.h
index e61c96da9cc..2ca79228185 100644
--- a/xpcom/string/public/string-template-def-char.h
+++ b/xpcom/string/public/string-template-def-char.h
@@ -3,8 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-// IWYU pragma: private, include "nsString.h"
+// IWYU pragma: private, include "nsStringGlue.h"
 
 #define CharT                               char
 #define CharT_is_char                       1
diff --git a/xpcom/string/public/string-template-def-unichar.h b/xpcom/string/public/string-template-def-unichar.h
index 4141e10df52..70a8f40e3a9 100644
--- a/xpcom/string/public/string-template-def-unichar.h
+++ b/xpcom/string/public/string-template-def-unichar.h
@@ -3,8 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-// IWYU pragma: private, include "nsString.h"
+// IWYU pragma: private, include "nsStringGlue.h"
 
 #define CharT                               PRUnichar
 #define CharT_is_PRUnichar                  1
diff --git a/xpcom/string/public/string-template-undef.h b/xpcom/string/public/string-template-undef.h
index 22bb7236b65..ba558c2a619 100644
--- a/xpcom/string/public/string-template-undef.h
+++ b/xpcom/string/public/string-template-undef.h
@@ -3,6 +3,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+// IWYU pragma: private, include "nsStringGlue.h"
 
 #undef CharT
 #undef CharT_is_PRUnichar