--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -3229,151 +3229,16 @@ nsRuleNode::CalcFontPointSize(int32_t aH
 
 
   if (1.0 < dFontSize) {
     return (nscoord)dFontSize;
   }
   return (nscoord)1;
 }
 
-
-//------------------------------------------------------------------------------
-//
-//------------------------------------------------------------------------------
-
-/* static */ nscoord
-nsRuleNode::FindNextSmallerFontSize(nscoord aFontSize, int32_t aBasePointSize,
-                                    nsPresContext* aPresContext,
-                                    nsFontSizeType aFontSizeType)
-{
-  int32_t index;
-  int32_t indexMin;
-  int32_t indexMax;
-  float relativePosition;
-  nscoord smallerSize;
-  nscoord indexFontSize = aFontSize; // XXX initialize to quell a spurious gcc3.2 warning
-  nscoord smallestIndexFontSize;
-  nscoord largestIndexFontSize;
-  nscoord smallerIndexFontSize;
-  nscoord largerIndexFontSize;
-
-  nscoord onePx = nsPresContext::CSSPixelsToAppUnits(1);
-
-  if (aFontSizeType == eFontSize_HTML) {
-    indexMin = 1;
-    indexMax = 7;
-  } else {
-    indexMin = 0;
-    indexMax = 6;
-  }
-
-  smallestIndexFontSize = CalcFontPointSize(indexMin, aBasePointSize, aPresContext, aFontSizeType);
-  largestIndexFontSize = CalcFontPointSize(indexMax, aBasePointSize, aPresContext, aFontSizeType);
-  if (aFontSize > smallestIndexFontSize) {
-    if (aFontSize < NSToCoordRound(float(largestIndexFontSize) * 1.5)) { // smaller will be in HTML table
-      // find largest index smaller than current
-      for (index = indexMax; index >= indexMin; index--) {
-        indexFontSize = CalcFontPointSize(index, aBasePointSize, aPresContext, aFontSizeType);
-        if (indexFontSize < aFontSize)
-          break;
-      }
-      // set up points beyond table for interpolation purposes
-      if (indexFontSize == smallestIndexFontSize) {
-        smallerIndexFontSize = indexFontSize - onePx;
-        largerIndexFontSize = CalcFontPointSize(index+1, aBasePointSize, aPresContext, aFontSizeType);
-      } else if (indexFontSize == largestIndexFontSize) {
-        smallerIndexFontSize = CalcFontPointSize(index-1, aBasePointSize, aPresContext, aFontSizeType);
-        largerIndexFontSize = NSToCoordRound(float(largestIndexFontSize) * 1.5);
-      } else {
-        smallerIndexFontSize = CalcFontPointSize(index-1, aBasePointSize, aPresContext, aFontSizeType);
-        largerIndexFontSize = CalcFontPointSize(index+1, aBasePointSize, aPresContext, aFontSizeType);
-      }
-      // compute the relative position of the parent size between the two closest indexed sizes
-      relativePosition = float(aFontSize - indexFontSize) / float(largerIndexFontSize - indexFontSize);
-      // set the new size to have the same relative position between the next smallest two indexed sizes
-      smallerSize = smallerIndexFontSize + NSToCoordRound(relativePosition * (indexFontSize - smallerIndexFontSize));
-    }
-    else {  // larger than HTML table, drop by 33%
-      smallerSize = NSToCoordRound(float(aFontSize) / 1.5);
-    }
-  }
-  else { // smaller than HTML table, drop by 1px
-    smallerSize = std::max(aFontSize - onePx, onePx);
-  }
-  return smallerSize;
-}
-
-//------------------------------------------------------------------------------
-//
-//------------------------------------------------------------------------------
-
-/* static */ nscoord
-nsRuleNode::FindNextLargerFontSize(nscoord aFontSize, int32_t aBasePointSize,
-                                   nsPresContext* aPresContext,
-                                   nsFontSizeType aFontSizeType)
-{
-  int32_t index;
-  int32_t indexMin;
-  int32_t indexMax;
-  float relativePosition;
-  nscoord adjustment;
-  nscoord largerSize;
-  nscoord indexFontSize = aFontSize; // XXX initialize to quell a spurious gcc3.2 warning
-  nscoord smallestIndexFontSize;
-  nscoord largestIndexFontSize;
-  nscoord smallerIndexFontSize;
-  nscoord largerIndexFontSize;
-
-  nscoord onePx = nsPresContext::CSSPixelsToAppUnits(1);
-
-  if (aFontSizeType == eFontSize_HTML) {
-    indexMin = 1;
-    indexMax = 7;
-  } else {
-    indexMin = 0;
-    indexMax = 6;
-  }
-
-  smallestIndexFontSize = CalcFontPointSize(indexMin, aBasePointSize, aPresContext, aFontSizeType);
-  largestIndexFontSize = CalcFontPointSize(indexMax, aBasePointSize, aPresContext, aFontSizeType);
-  if (aFontSize > (smallestIndexFontSize - onePx)) {
-    if (aFontSize < largestIndexFontSize) { // larger will be in HTML table
-      // find smallest index larger than current
-      for (index = indexMin; index <= indexMax; index++) {
-        indexFontSize = CalcFontPointSize(index, aBasePointSize, aPresContext, aFontSizeType);
-        if (indexFontSize > aFontSize)
-          break;
-      }
-      // set up points beyond table for interpolation purposes
-      if (indexFontSize == smallestIndexFontSize) {
-        smallerIndexFontSize = indexFontSize - onePx;
-        largerIndexFontSize = CalcFontPointSize(index+1, aBasePointSize, aPresContext, aFontSizeType);
-      } else if (indexFontSize == largestIndexFontSize) {
-        smallerIndexFontSize = CalcFontPointSize(index-1, aBasePointSize, aPresContext, aFontSizeType);
-        largerIndexFontSize = NSCoordSaturatingMultiply(largestIndexFontSize, 1.5);
-      } else {
-        smallerIndexFontSize = CalcFontPointSize(index-1, aBasePointSize, aPresContext, aFontSizeType);
-        largerIndexFontSize = CalcFontPointSize(index+1, aBasePointSize, aPresContext, aFontSizeType);
-      }
-      // compute the relative position of the parent size between the two closest indexed sizes
-      relativePosition = float(aFontSize - smallerIndexFontSize) / float(indexFontSize - smallerIndexFontSize);
-      // set the new size to have the same relative position between the next largest two indexed sizes
-      adjustment = NSCoordSaturatingNonnegativeMultiply(largerIndexFontSize - indexFontSize, relativePosition);
-      largerSize = NSCoordSaturatingAdd(indexFontSize, adjustment);
-    }
-    else {  // larger than HTML table, increase by 50%
-      largerSize = NSCoordSaturatingMultiply(aFontSize, 1.5);
-    }
-  }
-  else { // smaller than HTML table, increase by 1px
-    largerSize = NSCoordSaturatingAdd(aFontSize, onePx);
-  }
-  return largerSize;
-}
-
 struct SetFontSizeCalcOps : public css::BasicCoordCalcOps,
                             public css::FloatCoeffsAlreadyNormalizedOps
 {
   // Declare that we have floats as coefficients so that we unambiguously
   // resolve coeff_type (BasicCoordCalcOps and FloatCoeffsAlreadyNormalizedOps
   // both have |typedef float coeff_type|).
   typedef float coeff_type;
 
@@ -3472,30 +3337,20 @@ nsRuleNode::SetFontSize(nsPresContext* a
       // Note that relative units here use the parent's size unadjusted
       // for scriptlevel changes. A scriptlevel change between us and the parent
       // is simply ignored.
       nscoord parentSize = aParentSize;
       if (aParentFont->mAllowZoom) {
         parentSize = nsStyleFont::UnZoomText(aPresContext, parentSize);
       }
 
-      if (NS_STYLE_FONT_SIZE_LARGER == value) {
-        *aSize = FindNextLargerFontSize(parentSize,
-                         baseSize, aPresContext, eFontSize_CSS);
-
-        NS_ASSERTION(*aSize >= parentSize,
-                     "FindNextLargerFontSize failed");
-      }
-      else {
-        *aSize = FindNextSmallerFontSize(parentSize,
-                         baseSize, aPresContext, eFontSize_CSS);
-        NS_ASSERTION(*aSize < parentSize ||
-                     parentSize <= nsPresContext::CSSPixelsToAppUnits(1),
-                     "FindNextSmallerFontSize failed");
-      }
+      float factor = (NS_STYLE_FONT_SIZE_LARGER == value) ? 1.2f : (1.0f / 1.2f);
+
+      *aSize = parentSize * factor;
+
     } else {
       NS_NOTREACHED("unexpected value");
     }
   }
   else if (sizeValue->IsLengthUnit() ||
            sizeValue->GetUnit() == eCSSUnit_Percent ||
            sizeValue->IsCalcUnit()) {
     SetFontSizeCalcOps ops(aParentSize, aParentFont,

--- a/servo/components/style/properties/longhand/font.mako.rs
+++ b/servo/components/style/properties/longhand/font.mako.rs
@@ -763,16 +763,20 @@
             if let SpecifiedValue::Length(ref lop) = *self {
                 if let LengthOrPercentage::Percentage(pc) = *lop {
                     return Some(pc.0)
                 } else if let LengthOrPercentage::Length(ref nocalc) = *lop {
                     if let NoCalcLength::FontRelative(FontRelativeLength::Em(em)) = *nocalc {
                         return Some(em)
                     }
                 }
+            } else if let SpecifiedValue::Larger = *self {
+                return Some(1.2)
+            } else if let SpecifiedValue::Smaller = *self {
+                return Some(1./1.2)
             }
             None
         }
 
         /// Compute it against a given base font size
         pub fn to_computed_value_against(&self, context: &Context, base_size: FontBaseSize) -> Au {
             use values::specified::length::FontRelativeLength;
             match *self {