--- a/gfx/thebes/gfxMacPlatformFontList.h
+++ b/gfx/thebes/gfxMacPlatformFontList.h
@@ -104,18 +104,17 @@ public:
                             nsTArray<gfxFontFamily*>* aOutput,
                             gfxFontStyle* aStyle = nullptr,
                             gfxFloat aDevToCssSize = 1.0) override;
 
     // lookup the system font for a particular system font type and set
     // the name and style characteristics
     void LookupSystemFont(mozilla::LookAndFeel::FontID aSystemFontID,
                           nsAString& aSystemFontName,
-                          gfxFontStyle &aFontStyle,
-                          float aDevPixPerCSSPixel);
+                          gfxFontStyle &aFontStyle);
 
     // Values for the entryType field in FontFamilyListEntry records passed
     // from chrome to content process.
     enum FontFamilyEntryType {
         kStandardFontFamily = 0, // a standard installed font family
         kHiddenSystemFontFamily = 1, // hidden system family, not exposed to UI
         kTextSizeSystemFontFamily = 2, // name of 'system' font at text sizes
         kDisplaySizeSystemFontFamily = 3 // 'system' font at display sizes

--- a/gfx/thebes/gfxMacPlatformFontList.mm
+++ b/gfx/thebes/gfxMacPlatformFontList.mm
@@ -1262,18 +1262,17 @@ gfxMacPlatformFontList::FindAndAddFamili
 
     return gfxPlatformFontList::FindAndAddFamilies(aFamily, aOutput, aStyle,
                                                    aDevToCssSize);
 }
 
 void
 gfxMacPlatformFontList::LookupSystemFont(LookAndFeel::FontID aSystemFontID,
                                          nsAString& aSystemFontName,
-                                         gfxFontStyle &aFontStyle,
-                                         float aDevPixPerCSSPixel)
+                                         gfxFontStyle &aFontStyle)
 {
     // code moved here from widget/cocoa/nsLookAndFeel.mm
     NSFont *font = nullptr;
     char* systemFontName = nullptr;
     switch (aSystemFontID) {
         case LookAndFeel::eFont_MessageBox:
         case LookAndFeel::eFont_StatusBar:
         case LookAndFeel::eFont_List:
@@ -1326,18 +1325,17 @@ gfxMacPlatformFontList::LookupSystemFont
     aFontStyle.style =
         (traits & NSFontItalicTrait) ?  NS_FONT_STYLE_ITALIC : NS_FONT_STYLE_NORMAL;
     aFontStyle.weight =
         (traits & NSFontBoldTrait) ? NS_FONT_WEIGHT_BOLD : NS_FONT_WEIGHT_NORMAL;
     aFontStyle.stretch =
         (traits & NSFontExpandedTrait) ?
             NS_FONT_STRETCH_EXPANDED : (traits & NSFontCondensedTrait) ?
                 NS_FONT_STRETCH_CONDENSED : NS_FONT_STRETCH_NORMAL;
-    // convert size from css pixels to device pixels
-    aFontStyle.size = [font pointSize] * aDevPixPerCSSPixel;
+    aFontStyle.size = [font pointSize];
     aFontStyle.systemFont = true;
 }
 
 // used to load system-wide font info on off-main thread
 class MacFontInfo : public FontInfoData {
 public:
     MacFontInfo(bool aLoadOtherNames,
                 bool aLoadFaceNames,

--- a/gfx/thebes/gfxPlatformMac.cpp
+++ b/gfx/thebes/gfxPlatformMac.cpp
@@ -341,22 +341,20 @@ gfxPlatformMac::GetCommonFallbackFonts(u
 
     // Arial Unicode MS has lots of glyphs for obscure, use it as a last resort
     aFontList.AppendElement(kFontArialUnicodeMS);
 }
 
 /*static*/ void
 gfxPlatformMac::LookupSystemFont(mozilla::LookAndFeel::FontID aSystemFontID,
                                  nsAString& aSystemFontName,
-                                 gfxFontStyle& aFontStyle,
-                                 float aDevPixPerCSSPixel)
+                                 gfxFontStyle& aFontStyle)
 {
     gfxMacPlatformFontList* pfl = gfxMacPlatformFontList::PlatformFontList();
-    return pfl->LookupSystemFont(aSystemFontID, aSystemFontName, aFontStyle,
-                                 aDevPixPerCSSPixel);
+    return pfl->LookupSystemFont(aSystemFontID, aSystemFontName, aFontStyle);
 }
 
 uint32_t
 gfxPlatformMac::ReadAntiAliasingThreshold()
 {
     uint32_t threshold = 0;  // default == no threshold
 
     // first read prefs flag to determine whether to use the setting or not

--- a/gfx/thebes/gfxPlatformMac.h
+++ b/gfx/thebes/gfxPlatformMac.h
@@ -52,18 +52,17 @@ public:
                                         Script aRunScript,
                                         nsTArray<const char*>& aFontList) override;
 
     // lookup the system font for a particular system font type and set
     // the name and style characteristics
     static void
     LookupSystemFont(mozilla::LookAndFeel::FontID aSystemFontID,
                      nsAString& aSystemFontName,
-                     gfxFontStyle &aFontStyle,
-                     float aDevPixPerCSSPixel);
+                     gfxFontStyle &aFontStyle);
 
     virtual bool CanRenderContentToDataSurface() const override {
       return true;
     }
 
     virtual bool SupportsApzWheelInput() const override {
       return true;
     }

--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -3601,32 +3601,27 @@ nsRuleNode::SetFont(nsPresContext* aPres
 
   // Fall back to defaultVariableFont.
   nsFont systemFont = *defaultVariableFont;
   const nsCSSValue* systemFontValue = aRuleData->ValueForSystemFont();
   if (eCSSUnit_Enumerated == systemFontValue->GetUnit()) {
     gfxFontStyle fontStyle;
     LookAndFeel::FontID fontID =
       (LookAndFeel::FontID)systemFontValue->GetIntValue();
-    float devPerCSS =
-      (float)nsPresContext::AppUnitsPerCSSPixel() /
-      aPresContext->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom();
     nsAutoString systemFontName;
-    if (LookAndFeel::GetFont(fontID, systemFontName, fontStyle, devPerCSS)) {
+    if (LookAndFeel::GetFont(fontID, systemFontName, fontStyle)) {
       systemFontName.Trim("\"'");
       systemFont.fontlist = FontFamilyList(systemFontName, eUnquotedName);
       systemFont.fontlist.SetDefaultFontType(eFamily_none);
       systemFont.style = fontStyle.style;
       systemFont.systemFont = fontStyle.systemFont;
       systemFont.weight = fontStyle.weight;
       systemFont.stretch = fontStyle.stretch;
-      systemFont.size =
-        NSFloatPixelsToAppUnits(fontStyle.size,
-                                aPresContext->DeviceContext()->
-                                  AppUnitsPerDevPixelAtUnitFullZoom());
+      systemFont.size = nsPresContext::
+        CSSPixelsToAppUnits(static_cast<float>(fontStyle.size));
       //systemFont.langGroup = fontStyle.langGroup;
       systemFont.sizeAdjust = fontStyle.sizeAdjust;
     }
   }
 
   // font-family: font family list, enum, inherit
   const nsCSSValue* familyValue = aRuleData->ValueForFontFamily();
   NS_ASSERTION(eCSSUnit_Enumerated != familyValue->GetUnit(),

--- a/widget/LookAndFeel.h
+++ b/widget/LookAndFeel.h
@@ -556,20 +556,18 @@ public:
   /**
    * Retrieve the name and style of a system-theme font.  Returns true
    * if the system theme specifies this font, false if a default should
    * be used.  In the latter case neither aName nor aStyle is modified.
    *
    * @param aID    Which system-theme font is wanted.
    * @param aName  The name of the font to use.
    * @param aStyle Styling to apply to the font.
-   * @param aDevPixPerCSSPixel  Ratio of device pixels to CSS pixels
    */
-  static bool GetFont(FontID aID, nsString& aName, gfxFontStyle& aStyle,
-                      float aDevPixPerCSSPixel);
+  static bool GetFont(FontID aID, nsString& aName, gfxFontStyle& aStyle);
 
   /**
    * GetPasswordCharacter() returns a unicode character which should be used
    * for a masked character in password editor.  E.g., '*'.
    */
   static char16_t GetPasswordCharacter();
 
   /**

--- a/widget/android/nsLookAndFeel.cpp
+++ b/widget/android/nsLookAndFeel.cpp
@@ -452,24 +452,23 @@ nsLookAndFeel::GetFloatImpl(FloatID aID,
             break;
     }
     return rv;
 }
 
 /*virtual*/
 bool
 nsLookAndFeel::GetFontImpl(FontID aID, nsString& aFontName,
-                           gfxFontStyle& aFontStyle,
-                           float aDevPixPerCSSPixel)
+                           gfxFontStyle& aFontStyle)
 {
     aFontName.AssignLiteral("\"Droid Sans\"");
     aFontStyle.style = NS_FONT_STYLE_NORMAL;
     aFontStyle.weight = NS_FONT_WEIGHT_NORMAL;
     aFontStyle.stretch = NS_FONT_STRETCH_NORMAL;
-    aFontStyle.size = 9.0 * 96.0f / 72.0f * aDevPixPerCSSPixel;
+    aFontStyle.size = 9.0 * 96.0f / 72.0f;
     aFontStyle.systemFont = true;
     return true;
 }
 
 /*virtual*/
 bool
 nsLookAndFeel::GetEchoPasswordImpl()
 {

--- a/widget/android/nsLookAndFeel.h
+++ b/widget/android/nsLookAndFeel.h
@@ -12,18 +12,17 @@ class nsLookAndFeel: public nsXPLookAndF
 {
 public:
     nsLookAndFeel();
     virtual ~nsLookAndFeel();
 
     virtual nsresult NativeGetColor(ColorID aID, nscolor &aResult);
     virtual nsresult GetIntImpl(IntID aID, int32_t &aResult);
     virtual nsresult GetFloatImpl(FloatID aID, float &aResult);
-    virtual bool GetFontImpl(FontID aID, nsString& aName, gfxFontStyle& aStyle,
-                             float aDevPixPerCSSPixel);
+    virtual bool GetFontImpl(FontID aID, nsString& aName, gfxFontStyle& aStyle);
     virtual bool GetEchoPasswordImpl();
     virtual uint32_t GetPasswordMaskDelayImpl();
     virtual char16_t GetPasswordCharacterImpl();
 
 protected:
     static bool mInitializedSystemColors;
     static mozilla::AndroidSystemColors mSystemColors;
     static bool mInitializedShowPassword;

--- a/widget/cocoa/nsLookAndFeel.h
+++ b/widget/cocoa/nsLookAndFeel.h
@@ -11,18 +11,17 @@ class nsLookAndFeel: public nsXPLookAndF
 public:
   nsLookAndFeel();
   virtual ~nsLookAndFeel();
 
   virtual nsresult NativeGetColor(ColorID aID, nscolor &aResult);
   virtual nsresult GetIntImpl(IntID aID, int32_t &aResult);
   virtual nsresult GetFloatImpl(FloatID aID, float &aResult);
   virtual bool GetFontImpl(FontID aID, nsString& aFontName,
-                           gfxFontStyle& aFontStyle,
-                           float aDevPixPerCSSPixel);
+                           gfxFontStyle& aFontStyle);
   virtual char16_t GetPasswordCharacterImpl()
   {
     // unicode value for the bullet character, used for password textfields.
     return 0x2022;
   }
 
   static bool UseOverlayScrollbars();
 

--- a/widget/cocoa/nsLookAndFeel.mm
+++ b/widget/cocoa/nsLookAndFeel.mm
@@ -507,35 +507,33 @@ bool nsLookAndFeel::SystemWantsOverlaySc
 
 bool nsLookAndFeel::AllowOverlayScrollbarsOverlap()
 {
   return (UseOverlayScrollbars());
 }
 
 bool
 nsLookAndFeel::GetFontImpl(FontID aID, nsString &aFontName,
-                           gfxFontStyle &aFontStyle,
-                           float aDevPixPerCSSPixel)
+                           gfxFontStyle &aFontStyle)
 {
     NS_OBJC_BEGIN_TRY_ABORT_BLOCK_RETURN;
 
     // hack for now
     if (aID == eFont_Window || aID == eFont_Document) {
         aFontStyle.style      = NS_FONT_STYLE_NORMAL;
         aFontStyle.weight     = NS_FONT_WEIGHT_NORMAL;
         aFontStyle.stretch    = NS_FONT_STRETCH_NORMAL;
-        aFontStyle.size       = 14 * aDevPixPerCSSPixel;
+        aFontStyle.size       = 14;
         aFontStyle.systemFont = true;
 
         aFontName.AssignLiteral("sans-serif");
         return true;
     }
 
-    gfxPlatformMac::LookupSystemFont(aID, aFontName, aFontStyle,
-                                     aDevPixPerCSSPixel);
+    gfxPlatformMac::LookupSystemFont(aID, aFontName, aFontStyle);
 
     return true;
 
     NS_OBJC_END_TRY_ABORT_BLOCK_RETURN(false);
 }
 
 nsTArray<LookAndFeelInt>
 nsLookAndFeel::GetIntCacheImpl()

--- a/widget/gonk/nsLookAndFeel.cpp
+++ b/widget/gonk/nsLookAndFeel.cpp
@@ -426,18 +426,17 @@ nsLookAndFeel::GetFloatImpl(FloatID aID,
         res = NS_ERROR_FAILURE;
     }
   return res;
 }
 
 /*virtual*/
 bool
 nsLookAndFeel::GetFontImpl(FontID aID, nsString& aFontName,
-                           gfxFontStyle& aFontStyle,
-                           float aDevPixPerCSSPixel)
+                           gfxFontStyle& aFontStyle)
 {
     aFontName.AssignLiteral("\"Fira Sans\"");
     aFontStyle.style = NS_FONT_STYLE_NORMAL;
     aFontStyle.weight = NS_FONT_WEIGHT_NORMAL;
     aFontStyle.stretch = NS_FONT_STRETCH_NORMAL;
     aFontStyle.size = 9.0 * 96.0f / 72.0f;
     aFontStyle.systemFont = true;
     return true;

--- a/widget/gonk/nsLookAndFeel.h
+++ b/widget/gonk/nsLookAndFeel.h
@@ -20,18 +20,17 @@
 #include "nsXPLookAndFeel.h"
 
 class nsLookAndFeel : public nsXPLookAndFeel
 {
 public:
     nsLookAndFeel();
     virtual ~nsLookAndFeel();
 
-    virtual bool GetFontImpl(FontID aID, nsString& aName, gfxFontStyle& aStyle,
-                             float aDevPixPerCSSPixel);
+    virtual bool GetFontImpl(FontID aID, nsString& aName, gfxFontStyle& aStyle);
     virtual nsresult GetIntImpl(IntID aID, int32_t &aResult);
     virtual nsresult GetFloatImpl(FloatID aID, float &aResult);
     virtual bool GetEchoPasswordImpl();
     virtual uint32_t GetPasswordMaskDelayImpl();
     virtual char16_t GetPasswordCharacterImpl();
 
 protected:
     virtual nsresult NativeGetColor(ColorID aID, nscolor &aColor);

--- a/widget/gtk/nsLookAndFeel.cpp
+++ b/widget/gtk/nsLookAndFeel.cpp
@@ -993,18 +993,17 @@ GetSystemFontInfo(LookAndFeel::FontID aI
         gtk_widget_ensure_style(accel_label);
         GetSystemFontInfo(accel_label, aFontName, aFontStyle);
         g_object_unref(menu);
     }
 }
 
 bool
 nsLookAndFeel::GetFontImpl(FontID aID, nsString& aFontName,
-                           gfxFontStyle& aFontStyle,
-                           float aDevPixPerCSSPixel)
+                           gfxFontStyle& aFontStyle)
 {
   nsString *cachedFontName = nullptr;
   gfxFontStyle *cachedFontStyle = nullptr;
   bool *isCached = nullptr;
 
   switch (aID) {
     case eFont_Menu:         // css2
     case eFont_PullDownMenu: // css3
@@ -1050,17 +1049,16 @@ nsLookAndFeel::GetFontImpl(FontID aID, n
 
   if (!*isCached) {
     GetSystemFontInfo(aID, cachedFontName, cachedFontStyle);
     *isCached = true;
   }
 
   aFontName = *cachedFontName;
   aFontStyle = *cachedFontStyle;
-  aFontStyle.size *= aDevPixPerCSSPixel;
   return true;
 }
 
 void
 nsLookAndFeel::EnsureInit()
 {
     GdkColor colorValue;
     GdkColor *colorValuePtr;

--- a/widget/gtk/nsLookAndFeel.h
+++ b/widget/gtk/nsLookAndFeel.h
@@ -18,18 +18,17 @@ class nsLookAndFeel: public nsXPLookAndF
 public:
     nsLookAndFeel();
     virtual ~nsLookAndFeel();
 
     virtual nsresult NativeGetColor(ColorID aID, nscolor &aResult);
     virtual nsresult GetIntImpl(IntID aID, int32_t &aResult);
     virtual nsresult GetFloatImpl(FloatID aID, float &aResult);
     virtual bool GetFontImpl(FontID aID, nsString& aFontName,
-                             gfxFontStyle& aFontStyle,
-                             float aDevPixPerCSSPixel);
+                             gfxFontStyle& aFontStyle);
 
     virtual void RefreshImpl();
     virtual char16_t GetPasswordCharacterImpl();
     virtual bool GetEchoPasswordImpl();
 
 protected:
 #if (MOZ_WIDGET_GTK == 2)
     struct _GtkStyle *mStyle;

--- a/widget/nsXPLookAndFeel.cpp
+++ b/widget/nsXPLookAndFeel.cpp
@@ -935,21 +935,19 @@ LookAndFeel::GetInt(IntID aID, int32_t* 
 nsresult
 LookAndFeel::GetFloat(FloatID aID, float* aResult)
 {
   return nsLookAndFeel::GetInstance()->GetFloatImpl(aID, *aResult);
 }
 
 // static
 bool
-LookAndFeel::GetFont(FontID aID, nsString& aName, gfxFontStyle& aStyle,
-                     float aDevPixPerCSSPixel)
+LookAndFeel::GetFont(FontID aID, nsString& aName, gfxFontStyle& aStyle)
 {
-  return nsLookAndFeel::GetInstance()->GetFontImpl(aID, aName, aStyle,
-                                                   aDevPixPerCSSPixel);
+  return nsLookAndFeel::GetInstance()->GetFontImpl(aID, aName, aStyle);
 }
 
 // static
 char16_t
 LookAndFeel::GetPasswordCharacter()
 {
   return nsLookAndFeel::GetInstance()->GetPasswordCharacterImpl();
 }

--- a/widget/nsXPLookAndFeel.h
+++ b/widget/nsXPLookAndFeel.h
@@ -56,18 +56,17 @@ public:
   nsresult GetColorImpl(ColorID aID, bool aUseStandinsForNativeColors,
                         nscolor &aResult);
   virtual nsresult GetIntImpl(IntID aID, int32_t &aResult);
   virtual nsresult GetFloatImpl(FloatID aID, float &aResult);
 
   // This one is different: there are no override prefs (fixme?), so
   // there is no XP implementation, only per-system impls.
   virtual bool GetFontImpl(FontID aID, nsString& aName,
-                           gfxFontStyle& aStyle,
-                           float aDevPixPerCSSPixel) = 0;
+                           gfxFontStyle& aStyle) = 0;
 
   virtual void RefreshImpl();
 
   virtual char16_t GetPasswordCharacterImpl()
   {
     return char16_t('*');
   }
 

--- a/widget/uikit/nsLookAndFeel.h
+++ b/widget/uikit/nsLookAndFeel.h
@@ -13,18 +13,17 @@ class nsLookAndFeel: public nsXPLookAndF
 public:
     nsLookAndFeel();
     virtual ~nsLookAndFeel();
 
     virtual nsresult NativeGetColor(const ColorID aID, nscolor &aResult);
     virtual nsresult GetIntImpl(IntID aID, int32_t &aResult);
     virtual nsresult GetFloatImpl(FloatID aID, float &aResult);
     virtual bool GetFontImpl(FontID aID, nsString& aFontName,
-                             gfxFontStyle& aFontStyle,
-                             float aDevPixPerCSSPixel);
+                             gfxFontStyle& aFontStyle);
     virtual char16_t GetPasswordCharacterImpl()
     {
         // unicode value for the bullet character, used for password textfields.
         return 0x2022;
     }
 
     static bool UseOverlayScrollbars()
     {

--- a/widget/uikit/nsLookAndFeel.mm
+++ b/widget/uikit/nsLookAndFeel.mm
@@ -376,25 +376,24 @@ nsLookAndFeel::GetFloatImpl(FloatID aID,
       res = NS_ERROR_FAILURE;
   }
 
   return res;
 }
 
 bool
 nsLookAndFeel::GetFontImpl(FontID aID, nsString &aFontName,
-                           gfxFontStyle &aFontStyle,
-                           float aDevPixPerCSSPixel)
+                           gfxFontStyle &aFontStyle)
 {
     // hack for now
     if (aID == eFont_Window || aID == eFont_Document) {
         aFontStyle.style      = NS_FONT_STYLE_NORMAL;
         aFontStyle.weight     = NS_FONT_WEIGHT_NORMAL;
         aFontStyle.stretch    = NS_FONT_STRETCH_NORMAL;
-        aFontStyle.size       = 14 * aDevPixPerCSSPixel;
+        aFontStyle.size       = 14;
         aFontStyle.systemFont = true;
 
         aFontName.AssignLiteral("sans-serif");
         return true;
     }
 
     //TODO: implement more here?
     return false;

--- a/widget/windows/nsLookAndFeel.cpp
+++ b/widget/windows/nsLookAndFeel.cpp
@@ -645,24 +645,21 @@ GetSysFontInfo(HDC aHDC, LookAndFeel::Fo
     aFontName = name;
   }
 
   return true;
 }
 
 bool
 nsLookAndFeel::GetFontImpl(FontID anID, nsString &aFontName,
-                           gfxFontStyle &aFontStyle,
-                           float aDevPixPerCSSPixel)
+                           gfxFontStyle &aFontStyle)
 {
   HDC tdc = GetDC(nullptr);
   bool status = GetSysFontInfo(tdc, anID, aFontName, aFontStyle);
   ReleaseDC(nullptr, tdc);
-  // now convert the logical font size from GetSysFontInfo into device pixels for layout
-  aFontStyle.size *= aDevPixPerCSSPixel;
   return status;
 }
 
 /* virtual */
 char16_t
 nsLookAndFeel::GetPasswordCharacterImpl()
 {
 #define UNICODE_BLACK_CIRCLE_CHAR 0x25cf

--- a/widget/windows/nsLookAndFeel.h
+++ b/widget/windows/nsLookAndFeel.h
@@ -35,18 +35,17 @@ class nsLookAndFeel: public nsXPLookAndF
 public:
   nsLookAndFeel();
   virtual ~nsLookAndFeel();
 
   virtual nsresult NativeGetColor(ColorID aID, nscolor &aResult);
   virtual nsresult GetIntImpl(IntID aID, int32_t &aResult);
   virtual nsresult GetFloatImpl(FloatID aID, float &aResult);
   virtual bool GetFontImpl(FontID aID, nsString& aFontName,
-                           gfxFontStyle& aFontStyle,
-                           float aDevPixPerCSSPixel);
+                           gfxFontStyle& aFontStyle);
   virtual char16_t GetPasswordCharacterImpl();
 
   virtual nsTArray<LookAndFeelInt> GetIntCacheImpl();
   virtual void SetIntCacheImpl(const nsTArray<LookAndFeelInt>& aLookAndFeelIntCache);
 
 private:
   int32_t mUseAccessibilityTheme;
 };