--- a/layout/generic/nsFirstLetterFrame.cpp
+++ b/layout/generic/nsFirstLetterFrame.cpp
@@ -251,17 +251,23 @@ nsFirstLetterFrame::Reflow(nsPresContext
     ll->ReflowFrame(kid, aReflowStatus, &kidMetrics, pushedFrame);
     NS_ASSERTION(lineWM.IsVertical() == wm.IsVertical(),
                  "we're assuming we can mix sizes between lineWM and wm "
                  "since we shouldn't have orthogonal writing modes within "
                  "a line.");
     aMetrics.ISize(lineWM) = ll->EndSpan(this) + bp.IStartEnd(wm);
     ll->SetInFirstLetter(false);
 
-    nsLayoutUtils::SetBSizeFromFontMetrics(this, aMetrics, bp, lineWM, wm);
+    if (mStyleContext->StyleTextReset()->mInitialLetterSize != 0.0f) {
+      aMetrics.SetBlockStartAscent(kidMetrics.BlockStartAscent() +
+                                   bp.BStart(wm));
+      aMetrics.BSize(lineWM) = kidMetrics.BSize(lineWM) + bp.BStartEnd(wm);
+    } else {
+      nsLayoutUtils::SetBSizeFromFontMetrics(this, aMetrics, bp, lineWM, wm);
+    }
   }
 
   if (!NS_INLINE_IS_BREAK_BEFORE(aReflowStatus)) {
     // Create a continuation or remove existing continuations based on
     // the reflow completion status.
     if (NS_FRAME_IS_COMPLETE(aReflowStatus)) {
       if (aReflowInput.mLineLayout) {
         aReflowInput.mLineLayout->SetFirstLetterStyleOK(false);

--- a/layout/generic/nsTextFrame.cpp
+++ b/layout/generic/nsTextFrame.cpp
@@ -8767,16 +8767,24 @@ nsTextFrame::SetLength(int32_t aLength, 
 bool
 nsTextFrame::IsFloatingFirstLetterChild() const
 {
   nsIFrame* frame = GetParent();
   return frame && frame->IsFloating() &&
          frame->GetType() == nsGkAtoms::letterFrame;
 }
 
+bool
+nsTextFrame::IsInitialLetterChild() const
+{
+  nsIFrame* frame = GetParent();
+  return frame && frame->StyleTextReset()->mInitialLetterSize != 0.0f &&
+         frame->GetType() == nsGkAtoms::letterFrame;
+}
+
 struct NewlineProperty {
   int32_t mStartOffset;
   // The offset of the first \n after mStartOffset, or -1 if there is none
   int32_t mNewlineOffset;
 };
 
 void
 nsTextFrame::Reflow(nsPresContext*           aPresContext,
@@ -9045,19 +9053,20 @@ nsTextFrame::ReflowText(nsLineLayout& aL
     : -1;
   PropertyProvider provider(mTextRun, textStyle, frag, this, iter, length,
       lineContainer, xOffsetForTabs, nsTextFrame::eInflated);
 
   uint32_t transformedOffset = provider.GetStart().GetSkippedOffset();
 
   // The metrics for the text go in here
   gfxTextRun::Metrics textMetrics;
-  gfxFont::BoundingBoxType boundingBoxType = IsFloatingFirstLetterChild() ?
-                                               gfxFont::TIGHT_HINTED_OUTLINE_EXTENTS :
-                                               gfxFont::LOOSE_INK_EXTENTS;
+  gfxFont::BoundingBoxType boundingBoxType =
+    IsFloatingFirstLetterChild() || IsInitialLetterChild()
+    ? gfxFont::TIGHT_HINTED_OUTLINE_EXTENTS
+    : gfxFont::LOOSE_INK_EXTENTS;
   NS_ASSERTION(!(NS_REFLOW_CALC_BOUNDING_METRICS & aMetrics.mFlags),
                "We shouldn't be passed NS_REFLOW_CALC_BOUNDING_METRICS anymore");
 
   int32_t limitLength = length;
   int32_t forceBreak = aLineLayout.GetForcedBreakPosition(this);
   bool forceBreakAfter = false;
   if (forceBreak >= length) {
     forceBreakAfter = forceBreak == length;

--- a/layout/generic/nsTextFrame.h
+++ b/layout/generic/nsTextFrame.h
@@ -582,16 +582,18 @@ public:
 
   // Similar to Reflow(), but for use from nsLineLayout
   void ReflowText(nsLineLayout& aLineLayout, nscoord aAvailableWidth,
                   DrawTarget* aDrawTarget,
                   ReflowOutput& aMetrics, nsReflowStatus& aStatus);
 
   bool IsFloatingFirstLetterChild() const;
 
+  bool IsInitialLetterChild() const;
+
   virtual bool ComputeCustomOverflow(nsOverflowAreas& aOverflowAreas) override;
 
   void AssignJustificationGaps(const mozilla::JustificationAssignment& aAssign);
   mozilla::JustificationAssignment GetJustificationAssignment() const;
 
   uint32_t CountGraphemeClusters() const;
 
 protected: