diff --git a/layout/forms/nsFieldSetFrame.h b/layout/forms/nsFieldSetFrame.h
index 4b873340b83a0..1a75e1a18f6de 100644
--- a/layout/forms/nsFieldSetFrame.h
+++ b/layout/forms/nsFieldSetFrame.h
@@ -10,7 +10,6 @@
 #include "mozilla/Attributes.h"
 #include "ImgDrawResult.h"
 #include "nsContainerFrame.h"
-#include "nsIScrollableFrame.h"
 
 class nsFieldSetFrame final : public nsContainerFrame {
   typedef mozilla::image::ImgDrawResult ImgDrawResult;
diff --git a/layout/generic/ScrollbarActivity.cpp b/layout/generic/ScrollbarActivity.cpp
index 35281dc46ce97..ac5ded26f8cc2 100644
--- a/layout/generic/ScrollbarActivity.cpp
+++ b/layout/generic/ScrollbarActivity.cpp
@@ -12,7 +12,6 @@
 #include "nsContentUtils.h"
 #include "nsAString.h"
 #include "nsQueryFrame.h"
-#include "nsRefreshDriver.h"
 #include "nsComponentManagerUtils.h"
 #include "nsStyledElement.h"
 #include "mozilla/dom/Element.h"
diff --git a/layout/generic/WBRFrame.cpp b/layout/generic/WBRFrame.cpp
index 3ad733a2a4d36..8ff59820b0fbb 100644
--- a/layout/generic/WBRFrame.cpp
+++ b/layout/generic/WBRFrame.cpp
@@ -6,8 +6,6 @@
 
 /* rendering object for HTML <wbr> elements */
 
-#include "mozilla/PresShell.h"
-#include "nsHTMLParts.h"
 #include "nsIFrame.h"
 
 using namespace mozilla;
diff --git a/layout/generic/moz.build b/layout/generic/moz.build
index 2f71c47f0c82a..6ebf3b8121459 100644
--- a/layout/generic/moz.build
+++ b/layout/generic/moz.build
@@ -270,3 +270,5 @@ if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
 
 if CONFIG["CC_TYPE"] in ("clang", "gcc"):
     CXXFLAGS += ["-Wno-error=shadow"]
+
+REQUIRES_UNIFIED_BUILD = True
diff --git a/layout/generic/nsAbsoluteContainingBlock.cpp b/layout/generic/nsAbsoluteContainingBlock.cpp
index 8d929202200f1..a1a067fb55cc7 100644
--- a/layout/generic/nsAbsoluteContainingBlock.cpp
+++ b/layout/generic/nsAbsoluteContainingBlock.cpp
@@ -11,7 +11,6 @@
 
 #include "nsAbsoluteContainingBlock.h"
 
-#include "nsAtomicContainerFrame.h"
 #include "nsContainerFrame.h"
 #include "nsGkAtoms.h"
 #include "mozilla/CSSAlignUtils.h"
diff --git a/layout/generic/nsBackdropFrame.cpp b/layout/generic/nsBackdropFrame.cpp
index 20d3fcd368ad1..1b39ab3184aaf 100644
--- a/layout/generic/nsBackdropFrame.cpp
+++ b/layout/generic/nsBackdropFrame.cpp
@@ -8,7 +8,6 @@
 
 #include "nsBackdropFrame.h"
 
-#include "mozilla/PresShell.h"
 #include "nsDisplayList.h"
 
 using namespace mozilla;
diff --git a/layout/generic/nsBlockReflowContext.h b/layout/generic/nsBlockReflowContext.h
index 82171c55760b8..b7521f0a6e8c9 100644
--- a/layout/generic/nsBlockReflowContext.h
+++ b/layout/generic/nsBlockReflowContext.h
@@ -14,7 +14,6 @@
 class nsIFrame;
 class nsLineBox;
 class nsPresContext;
-class nsReflowStatus;
 namespace mozilla {
 class BlockReflowInput;
 }  // namespace mozilla
diff --git a/layout/generic/nsColumnSetFrame.cpp b/layout/generic/nsColumnSetFrame.cpp
index df94e0e875a43..90dc77ef5a1c2 100644
--- a/layout/generic/nsColumnSetFrame.cpp
+++ b/layout/generic/nsColumnSetFrame.cpp
@@ -14,8 +14,6 @@
 #include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/ToString.h"
 #include "nsCSSRendering.h"
-#include "nsDisplayList.h"
-#include "nsLayoutUtils.h"
 
 using namespace mozilla;
 using namespace mozilla::layout;
diff --git a/layout/generic/nsColumnSetFrame.h b/layout/generic/nsColumnSetFrame.h
index 576772c1b6e3f..b768782abdfb2 100644
--- a/layout/generic/nsColumnSetFrame.h
+++ b/layout/generic/nsColumnSetFrame.h
@@ -12,8 +12,6 @@
 #include "mozilla/Attributes.h"
 #include "nsContainerFrame.h"
 
-class nsCSSBorderRenderer;
-
 /**
  * nsColumnSetFrame implements CSS multi-column layout.
  * @note nsColumnSetFrame keeps true overflow containers in the normal flow
diff --git a/layout/generic/nsContainerFrame.cpp b/layout/generic/nsContainerFrame.cpp
index 4bd36733433cc..3b29555427a93 100644
--- a/layout/generic/nsContainerFrame.cpp
+++ b/layout/generic/nsContainerFrame.cpp
@@ -49,7 +49,6 @@ using namespace mozilla::layout;
 
 using mozilla::gfx::ColorPattern;
 using mozilla::gfx::DeviceColor;
-using mozilla::gfx::DrawTarget;
 using mozilla::gfx::Rect;
 using mozilla::gfx::sRGBColor;
 using mozilla::gfx::ToDeviceColor;
diff --git a/layout/generic/nsIFrame.cpp b/layout/generic/nsIFrame.cpp
index a4e6c6d5bb0af..e08b5ade8599e 100644
--- a/layout/generic/nsIFrame.cpp
+++ b/layout/generic/nsIFrame.cpp
@@ -8937,6 +8937,7 @@ nsresult nsIFrame::PeekOffset(nsPeekOffsetStruct* aPos) {
       return NS_ERROR_FAILURE;
     }
   }
+  return NS_OK;
 }
 
 nsIFrame::FrameSearchResult nsIFrame::PeekOffsetNoAmount(bool aForward,
diff --git a/layout/generic/nsImageMap.cpp b/layout/generic/nsImageMap.cpp
index 846373143da9e..0dddeb1e5de83 100644
--- a/layout/generic/nsImageMap.cpp
+++ b/layout/generic/nsImageMap.cpp
@@ -23,7 +23,6 @@
 #include "nsIContentInlines.h"
 #include "nsIScriptError.h"
 #include "nsContentUtils.h"
-#include "nsLayoutUtils.h"
 #include "ImageLayers.h"
 
 #ifdef ACCESSIBILITY
diff --git a/layout/generic/nsRubyFrame.cpp b/layout/generic/nsRubyFrame.cpp
index e52b5594b12f7..26b57d87d5801 100644
--- a/layout/generic/nsRubyFrame.cpp
+++ b/layout/generic/nsRubyFrame.cpp
@@ -14,7 +14,6 @@
 #include "mozilla/PresShell.h"
 #include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/WritingModes.h"
-#include "nsLayoutUtils.h"
 #include "nsLineLayout.h"
 #include "nsPresContext.h"
 #include "nsContainerFrameInlines.h"
diff --git a/layout/generic/nsRubyTextContainerFrame.cpp b/layout/generic/nsRubyTextContainerFrame.cpp
index eeb1f50f9ffc8..57bfb4cc209db 100644
--- a/layout/generic/nsRubyTextContainerFrame.cpp
+++ b/layout/generic/nsRubyTextContainerFrame.cpp
@@ -12,7 +12,6 @@
 #include "mozilla/PresShell.h"
 #include "mozilla/UniquePtr.h"
 #include "mozilla/WritingModes.h"
-#include "nsLayoutUtils.h"
 #include "nsLineLayout.h"
 #include "nsPresContext.h"
 
diff --git a/layout/xul/nsIScrollbarMediator.h b/layout/xul/nsIScrollbarMediator.h
index 699d810a9854d..fffc74f346dd1 100644
--- a/layout/xul/nsIScrollbarMediator.h
+++ b/layout/xul/nsIScrollbarMediator.h
@@ -7,7 +7,6 @@
 #ifndef nsIScrollbarMediator_h___
 #define nsIScrollbarMediator_h___
 
-#include "mozilla/ScrollTypes.h"
 #include "nsQueryFrame.h"
 #include "nsCoord.h"