diff --git a/gfx/src/X11Util.h b/gfx/src/X11Util.h
index 8fd42f0dd9ca..9659a0004b22 100644
--- a/gfx/src/X11Util.h
+++ b/gfx/src/X11Util.h
@@ -44,8 +44,8 @@ DefaultXDisplay()
 /**
  * Sets *aVisual to point to aDisplay's Visual struct corresponding to
  * aVisualID, and *aDepth to its depth.  When aVisualID is None, these are set
- * to NULL and 0 respectively.  Both out-parameter pointers are assumed
- * non-NULL.
+ * to nullptr and 0 respectively.  Both out-parameter pointers are assumed
+ * non-nullptr.
  */
 void
 FindVisualAndDepth(Display* aDisplay, VisualID aVisualID,
@@ -72,8 +72,8 @@ template <typename T>
 struct ScopedXFreePtrTraits
 {
   typedef T *type;
-  static T *empty() { return NULL; }
-  static void release(T *ptr) { if (ptr!=NULL) XFree(ptr); }
+  static T *empty() { return nullptr; }
+  static void release(T *ptr) { if (ptr != nullptr) XFree(ptr); }
 };
 SCOPED_TEMPLATE(ScopedXFree, ScopedXFreePtrTraits)
 
diff --git a/gfx/src/nsDeviceContext.cpp b/gfx/src/nsDeviceContext.cpp
index dc917ab76d84..d81e66adacb6 100644
--- a/gfx/src/nsDeviceContext.cpp
+++ b/gfx/src/nsDeviceContext.cpp
@@ -276,7 +276,7 @@ nsDeviceContext::FontMetricsDeleted(const nsFontMetrics* aFontMetrics)
 bool
 nsDeviceContext::IsPrinterSurface()
 {
-    return(mPrintingSurface != NULL);
+    return mPrintingSurface != nullptr;
 }
 
 void
diff --git a/gfx/src/nsDeviceContext.h b/gfx/src/nsDeviceContext.h
index d94b88d14609..b97b53f56aac 100644
--- a/gfx/src/nsDeviceContext.h
+++ b/gfx/src/nsDeviceContext.h
@@ -163,7 +163,7 @@ public:
      * EndDocument() or AbortDocument().
      *
      * @param aTitle - title of Document
-     * @param aPrintToFileName - name of file to print to, if NULL
+     * @param aPrintToFileName - name of file to print to, if nullptr
      * then don't print to file
      * @param aStartPage - starting page number (must be greater than zero)
      * @param aEndPage - ending page number (must be less than or
diff --git a/gfx/src/nsScriptableRegion.cpp b/gfx/src/nsScriptableRegion.cpp
index 806e2d9ec498..889f652204f8 100644
--- a/gfx/src/nsScriptableRegion.cpp
+++ b/gfx/src/nsScriptableRegion.cpp
@@ -139,10 +139,10 @@ NS_IMETHODIMP nsScriptableRegion::GetRects(JSContext* aCx, JS::Value* aRects)
   const nsIntRect *rect;
 
   while ((rect = iter.Next())) {
-    if (!JS_DefineElement(aCx, destArray, n, INT_TO_JSVAL(rect->x), NULL, NULL, JSPROP_ENUMERATE) ||
-        !JS_DefineElement(aCx, destArray, n + 1, INT_TO_JSVAL(rect->y), NULL, NULL, JSPROP_ENUMERATE) ||
-        !JS_DefineElement(aCx, destArray, n + 2, INT_TO_JSVAL(rect->width), NULL, NULL, JSPROP_ENUMERATE) ||
-        !JS_DefineElement(aCx, destArray, n + 3, INT_TO_JSVAL(rect->height), NULL, NULL, JSPROP_ENUMERATE)) {
+    if (!JS_DefineElement(aCx, destArray, n, INT_TO_JSVAL(rect->x), nullptr, nullptr, JSPROP_ENUMERATE) ||
+        !JS_DefineElement(aCx, destArray, n + 1, INT_TO_JSVAL(rect->y), nullptr, nullptr, JSPROP_ENUMERATE) ||
+        !JS_DefineElement(aCx, destArray, n + 2, INT_TO_JSVAL(rect->width), nullptr, nullptr, JSPROP_ENUMERATE) ||
+        !JS_DefineElement(aCx, destArray, n + 3, INT_TO_JSVAL(rect->height), nullptr, nullptr, JSPROP_ENUMERATE)) {
       return NS_ERROR_FAILURE;
     }
     n += 4;
diff --git a/gfx/src/nsThebesGfxFactory.cpp b/gfx/src/nsThebesGfxFactory.cpp
index 839f90424cdc..bf1bcd767452 100644
--- a/gfx/src/nsThebesGfxFactory.cpp
+++ b/gfx/src/nsThebesGfxFactory.cpp
@@ -51,17 +51,17 @@ NS_DEFINE_NAMED_CID(NS_SCRIPTABLE_REGION_CID);
 NS_DEFINE_NAMED_CID(NS_GFX_INITIALIZATION_CID);
 
 static const mozilla::Module::CIDEntry kThebesCIDs[] = {
-    { &kNS_FONT_ENUMERATOR_CID, false, NULL, nsThebesFontEnumeratorConstructor },
-    { &kNS_SCRIPTABLE_REGION_CID, false, NULL, nsScriptableRegionConstructor },
-    { &kNS_GFX_INITIALIZATION_CID, false, NULL, GfxInitializationConstructor },
-    { NULL }
+    { &kNS_FONT_ENUMERATOR_CID, false, nullptr, nsThebesFontEnumeratorConstructor },
+    { &kNS_SCRIPTABLE_REGION_CID, false, nullptr, nsScriptableRegionConstructor },
+    { &kNS_GFX_INITIALIZATION_CID, false, nullptr, GfxInitializationConstructor },
+    { nullptr }
 };
 
 static const mozilla::Module::ContractIDEntry kThebesContracts[] = {
     { "@mozilla.org/gfx/fontenumerator;1", &kNS_FONT_ENUMERATOR_CID },
     { "@mozilla.org/gfx/region;1", &kNS_SCRIPTABLE_REGION_CID },
     { "@mozilla.org/gfx/init;1", &kNS_GFX_INITIALIZATION_CID },
-    { NULL }
+    { nullptr }
 };
 
 static void
@@ -74,9 +74,9 @@ static const mozilla::Module kThebesModule = {
     mozilla::Module::kVersion,
     kThebesCIDs,
     kThebesContracts,
-    NULL,
-    NULL,
-    NULL,
+    nullptr,
+    nullptr,
+    nullptr,
     nsThebesGfxModuleDtor
 };