diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 90d355dd2869..79e1d987d8a6 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -5051,8 +5051,6 @@ GetDefiniteSize(const nsStyleCoord&       aStyle,
         nscoord pb = aIsInlineAxis ? aPercentageBasis.value().ISize(wm)
                                    : aPercentageBasis.value().BSize(wm);
         if (pb == NS_UNCONSTRAINEDSIZE) {
-          // XXXmats given that we're calculating an intrinsic size here,
-          // maybe we should back-compute the calc-size using AddPercents?
           return false;
         }
         *aResult = std::max(0, calc->mLength +
@@ -5296,12 +5294,9 @@ AddIntrinsicSizeOffset(gfxContext* aRenderingContext,
   nscoord result = aContentSize;
   nscoord min = aContentMinSize;
   nscoord coordOutsideSize = 0;
-  float pctOutsideSize = 0;
-  float pctTotal = 0.0f;
 
   if (!(aFlags & nsLayoutUtils::IGNORE_PADDING)) {
     coordOutsideSize += aOffsets.hPadding;
-    pctOutsideSize += aOffsets.hPctPadding;
   }
 
   coordOutsideSize += aOffsets.hBorder;
@@ -5309,21 +5304,15 @@ AddIntrinsicSizeOffset(gfxContext* aRenderingContext,
   if (aBoxSizing == StyleBoxSizing::Border) {
     min += coordOutsideSize;
     result = NSCoordSaturatingAdd(result, coordOutsideSize);
-    pctTotal += pctOutsideSize;
 
     coordOutsideSize = 0;
-    pctOutsideSize = 0.0f;
   }
 
   coordOutsideSize += aOffsets.hMargin;
-  pctOutsideSize += aOffsets.hPctMargin;
 
   min += coordOutsideSize;
   result = NSCoordSaturatingAdd(result, coordOutsideSize);
-  pctTotal += pctOutsideSize;
 
-  const bool shouldAddPercent = aType == nsLayoutUtils::PREF_ISIZE ||
-                                (aFlags & nsLayoutUtils::ADD_PERCENTS);
   nscoord size;
   if (aType == nsLayoutUtils::MIN_ISIZE &&
       (((aStyleSize.HasPercent() || aStyleMaxSize.HasPercent()) &&
@@ -5341,18 +5330,6 @@ AddIntrinsicSizeOffset(gfxContext* aRenderingContext,
              GetIntrinsicCoord(aStyleSize, aRenderingContext, aFrame,
                                PROP_WIDTH, size)) {
     result = size + coordOutsideSize;
-    if (shouldAddPercent) {
-      result = nsLayoutUtils::AddPercents(result, pctOutsideSize);
-    }
-  } else {
-    // NOTE: We could really do a lot better for percents and for some
-    // cases of calc() containing percent (certainly including any where
-    // the coefficient on the percent is positive and there are no max()
-    // expressions).  However, doing better for percents wouldn't be
-    // backwards compatible.
-    if (shouldAddPercent) {
-      result = nsLayoutUtils::AddPercents(result, pctTotal);
-    }
   }
 
   nscoord maxSize = aFixedMaxSize ? *aFixedMaxSize : 0;
@@ -5360,9 +5337,6 @@ AddIntrinsicSizeOffset(gfxContext* aRenderingContext,
       GetIntrinsicCoord(aStyleMaxSize, aRenderingContext, aFrame,
                         PROP_MAX_WIDTH, maxSize)) {
     maxSize += coordOutsideSize;
-    if (shouldAddPercent) {
-      maxSize = nsLayoutUtils::AddPercents(maxSize, pctOutsideSize);
-    }
     if (result > maxSize) {
       result = maxSize;
     }
@@ -5373,17 +5347,11 @@ AddIntrinsicSizeOffset(gfxContext* aRenderingContext,
       GetIntrinsicCoord(aStyleMinSize, aRenderingContext, aFrame,
                         PROP_MIN_WIDTH, minSize)) {
     minSize += coordOutsideSize;
-    if (shouldAddPercent) {
-      minSize = nsLayoutUtils::AddPercents(minSize, pctOutsideSize);
-    }
     if (result < minSize) {
       result = minSize;
     }
   }
 
-  if (shouldAddPercent) {
-    min = nsLayoutUtils::AddPercents(min, pctTotal);
-  }
   if (result < min) {
     result = min;
   }
@@ -5400,9 +5368,6 @@ AddIntrinsicSizeOffset(gfxContext* aRenderingContext,
                                                      : devSize.width);
     // GetMinimumWidgetSize() returns a border-box width.
     themeSize += aOffsets.hMargin;
-    if (shouldAddPercent) {
-      themeSize = nsLayoutUtils::AddPercents(themeSize, aOffsets.hPctMargin);
-    }
     if (themeSize > result || !canOverride) {
       result = themeSize;
     }
@@ -5697,9 +5662,7 @@ nsLayoutUtils::MinSizeContributionForAxis(PhysicalAxis        aAxis,
                 aWM.IsVertical() ? "vertical" : "horizontal");
 #endif
 
-  // Note: this method is only meant for grid/flex items which always
-  // include percentages in their intrinsic size.
-  aFlags |= nsLayoutUtils::ADD_PERCENTS;
+  // Note: this method is only meant for grid/flex items.
   const nsStylePosition* const stylePos = aFrame->StylePosition();
   const nsStyleCoord* style = aAxis == eAxisHorizontal ? &stylePos->mMinWidth
                                                        : &stylePos->mMinHeight;
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index 59f3686ffc67..0c7422be6aa5 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -1423,7 +1423,6 @@ public:
     IGNORE_PADDING = 0x01,
     BAIL_IF_REFLOW_NEEDED = 0x02, // returns NS_INTRINSIC_WIDTH_UNKNOWN if so
     MIN_INTRINSIC_ISIZE = 0x04, // use min-width/height instead of width/height
-    ADD_PERCENTS = 0x08, // apply AddPercents also for MIN_ISIZE
   };
   static nscoord
   IntrinsicForAxis(mozilla::PhysicalAxis aAxis,
@@ -1464,23 +1463,6 @@ public:
                                             IntrinsicISizeType    aType,
                                             uint32_t              aFlags = 0);
 
-  /**
-   * This function increases an initial intrinsic size, 'aCurrent', according
-   * to the given 'aPercent', such that the size-increase makes up exactly
-   * 'aPercent' percent of the returned value.  If 'aPercent' or 'aCurrent' are
-   * less than or equal to zero the original 'aCurrent' value is returned.
-   * If 'aPercent' is greater than or equal to 1.0 the value nscoord_MAX is
-   * returned.
-   */
-  static nscoord AddPercents(nscoord aCurrent, float aPercent)
-  {
-    if (aPercent > 0.0f && aCurrent > 0) {
-      return MOZ_UNLIKELY(aPercent >= 1.0f) ? nscoord_MAX
-        : NSToCoordRound(float(aCurrent) / (1.0f - aPercent));
-    }
-    return aCurrent;
-  }
-
   /*
    * Convert nsStyleCoord to nscoord when percentages depend on the
    * containing block size.
diff --git a/layout/generic/nsGridContainerFrame.cpp b/layout/generic/nsGridContainerFrame.cpp
index 5a4c8a2f3336..bec0672ea686 100644
--- a/layout/generic/nsGridContainerFrame.cpp
+++ b/layout/generic/nsGridContainerFrame.cpp
@@ -3582,8 +3582,7 @@ ContentContribution(const GridItemInfo&       aGridItem,
   PhysicalAxis axis(aCBWM.PhysicalAxis(aAxis));
   nscoord size = nsLayoutUtils::IntrinsicForAxis(axis, aRC, child, aConstraint,
                    aPercentageBasis,
-                   aFlags | nsLayoutUtils::BAIL_IF_REFLOW_NEEDED |
-                            nsLayoutUtils::ADD_PERCENTS,
+                   aFlags | nsLayoutUtils::BAIL_IF_REFLOW_NEEDED,
                    aMinSizeClamp);
   if (size == NS_INTRINSIC_WIDTH_UNKNOWN) {
     // We need to reflow the child to find its BSize contribution.
@@ -3620,15 +3619,7 @@ ContentContribution(const GridItemInfo&       aGridItem,
     LogicalSize availableSize(childWM, availISize, availBSize);
     size = ::MeasuringReflow(child, aState.mReflowInput, aRC, availableSize,
                              cbSize, iMinSizeClamp, bMinSizeClamp);
-    nsIFrame::IntrinsicISizeOffsetData offsets = child->IntrinsicBSizeOffsets();
-    size += offsets.hMargin;
-    auto percent = offsets.hPctMargin;
-    if (availBSize == NS_UNCONSTRAINEDSIZE) {
-      // We always want to add in percent padding too, unless we already did so
-      // using a resolved column size above.
-      percent += offsets.hPctPadding;
-    }
-    size = nsLayoutUtils::AddPercents(size, percent);
+    size += child->GetLogicalUsedMargin(childWM).BStartEnd(childWM);
     nscoord overflow = size - aMinSizeClamp;
     if (MOZ_UNLIKELY(overflow > 0)) {
       nscoord contentSize = child->ContentBSize(childWM);