diff --git a/dom/chrome-webidl/Flex.webidl b/dom/chrome-webidl/Flex.webidl
index 25092bb5b81d7..ed14a4ea59dad 100644
--- a/dom/chrome-webidl/Flex.webidl
+++ b/dom/chrome-webidl/Flex.webidl
@@ -83,6 +83,7 @@ enum FlexItemClampState {
 interface FlexItemValues
 {
   readonly attribute Node? node;
+  readonly attribute DOMRectReadOnly frameRect;
   readonly attribute double mainBaseSize;
   readonly attribute double mainDeltaSize;
   readonly attribute double mainMinSize;
diff --git a/dom/flex/FlexItemValues.cpp b/dom/flex/FlexItemValues.cpp
index f961846b41b5e..84088703a08c7 100644
--- a/dom/flex/FlexItemValues.cpp
+++ b/dom/flex/FlexItemValues.cpp
@@ -12,7 +12,8 @@
 namespace mozilla {
 namespace dom {
 
-NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(FlexItemValues, mParent)
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(FlexItemValues, mParent, mNode,
+                                      mFrameRect)
 NS_IMPL_CYCLE_COLLECTING_ADDREF(FlexItemValues)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(FlexItemValues)
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(FlexItemValues)
@@ -49,6 +50,14 @@ FlexItemValues::FlexItemValues(FlexLineValues* aParent,
   // going to keep it around.
   mNode = aItem->mNode;
 
+  // Since mNode might be null, we associate the mFrameRect with
+  // our parent.
+  mFrameRect = new DOMRectReadOnly(mParent,
+    nsPresContext::AppUnitsToDoubleCSSPixels(aItem->mFrameRect.X()),
+    nsPresContext::AppUnitsToDoubleCSSPixels(aItem->mFrameRect.Y()),
+    nsPresContext::AppUnitsToDoubleCSSPixels(aItem->mFrameRect.Width()),
+    nsPresContext::AppUnitsToDoubleCSSPixels(aItem->mFrameRect.Height()));
+
   // Convert app unit sizes to css pixel sizes.
   mMainBaseSize = nsPresContext::AppUnitsToDoubleCSSPixels(
     aItem->mMainBaseSize);
@@ -76,6 +85,12 @@ FlexItemValues::GetNode() const
   return mNode;
 }
 
+DOMRectReadOnly*
+FlexItemValues::FrameRect() const
+{
+  return mFrameRect;
+}
+
 double
 FlexItemValues::MainBaseSize() const
 {
diff --git a/dom/flex/FlexItemValues.h b/dom/flex/FlexItemValues.h
index 7b5c78429df68..7d1f5977b1bdc 100644
--- a/dom/flex/FlexItemValues.h
+++ b/dom/flex/FlexItemValues.h
@@ -39,6 +39,7 @@ class FlexItemValues : public nsISupports
   }
 
   nsINode* GetNode() const;
+  DOMRectReadOnly* FrameRect() const;
   double MainBaseSize() const;
   double MainDeltaSize() const;
   double MainMinSize() const;
@@ -50,6 +51,7 @@ class FlexItemValues : public nsISupports
 protected:
   RefPtr<FlexLineValues> mParent;
   RefPtr<nsINode> mNode;
+  RefPtr<DOMRectReadOnly> mFrameRect;
 
   // These sizes are all CSS pixel units.
   double mMainBaseSize;
diff --git a/layout/generic/nsFlexContainerFrame.cpp b/layout/generic/nsFlexContainerFrame.cpp
index 4add9657ea859..8f72fab1c2bbd 100644
--- a/layout/generic/nsFlexContainerFrame.cpp
+++ b/layout/generic/nsFlexContainerFrame.cpp
@@ -4849,14 +4849,9 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
 
         itemInfo->mNode = content;
 
-        // mMainBaseSize and itemInfo->mMainDeltaSize will
-        // be filled out in ResolveFlexibleLengths().
-
-        // Other FlexItem properties can be captured now.
-        itemInfo->mMainMinSize = item->GetMainMinSize();
-        itemInfo->mMainMaxSize = item->GetMainMaxSize();
-        itemInfo->mCrossMinSize = item->GetCrossMinSize();
-        itemInfo->mCrossMaxSize = item->GetCrossMaxSize();
+        // itemInfo->mMainBaseSize and mMainDeltaSize will be filled out
+        // in ResolveFlexibleLengths(). Other measurements will be captured
+        // at the end of this function.
       }
     }
   }
@@ -5261,7 +5256,7 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
 
   NS_FRAME_SET_TRUNCATION(aStatus, aReflowInput, aDesiredSize)
 
-  // Finally update our line sizing values in our containerInfo.
+  // Finally update our line and item measurements in our containerInfo.
   if (MOZ_UNLIKELY(containerInfo)) {
     lineIndex = 0;
     for (const FlexLine* line = lines.getFirst(); line;
@@ -5271,6 +5266,17 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
       lineInfo.mCrossSize = line->GetLineCrossSize();
       lineInfo.mFirstBaselineOffset = line->GetFirstBaselineOffset();
       lineInfo.mLastBaselineOffset = line->GetLastBaselineOffset();
+
+      uint32_t itemIndex = 0;
+      for (const FlexItem* item = line->GetFirstItem(); item;
+           item = item->getNext(), ++itemIndex) {
+        ComputedFlexItemInfo& itemInfo = lineInfo.mItems[itemIndex];
+        itemInfo.mFrameRect = item->Frame()->GetRect();
+        itemInfo.mMainMinSize = item->GetMainMinSize();
+        itemInfo.mMainMaxSize = item->GetMainMaxSize();
+        itemInfo.mCrossMinSize = item->GetCrossMinSize();
+        itemInfo.mCrossMaxSize = item->GetCrossMaxSize();
+      }
     }
   }
 }
diff --git a/layout/generic/nsFlexContainerFrame.h b/layout/generic/nsFlexContainerFrame.h
index 9bf1d820977b8..20e9c3ae3a2e2 100644
--- a/layout/generic/nsFlexContainerFrame.h
+++ b/layout/generic/nsFlexContainerFrame.h
@@ -33,6 +33,7 @@ nsContainerFrame* NS_NewFlexContainerFrame(nsIPresShell* aPresShell,
 struct ComputedFlexItemInfo
 {
   nsCOMPtr<nsINode> mNode;
+  nsRect mFrameRect;
   /**
    * mMainBaseSize is a measure of the size of the item in the main
    * axis before the flex sizing algorithm is applied. In the spec,