diff --git a/layout/reftests/xul/reftest.list b/layout/reftests/xul/reftest.list
--- a/layout/reftests/xul/reftest.list
+++ b/layout/reftests/xul/reftest.list
@@ -70,10 +70,12 @@
 skip == chrome://reftest/content/xul/treecell-image-svg-1b.xhtml chrome://reftest/content/xul/treecell-image-svg-1-ref.xhtml # bug 1218954
 
 != chrome://reftest/content/xul/treetwisty-svg-context-paint-1-not-ref.xhtml chrome://reftest/content/xul/treetwisty-svg-context-paint-1-ref.xhtml
 test-pref(svg.context-properties.content.enabled,true) fuzzy(0-26,0-2) == chrome://reftest/content/xul/treetwisty-svg-context-paint-1.xhtml chrome://reftest/content/xul/treetwisty-svg-context-paint-1-ref.xhtml
 
+== chrome://reftest/content/xul/tree-scrollbar-height-change.xhtml chrome://reftest/content/xul/tree-scrollbar-height-change-ref.xhtml
+
 # resizer (non-native-themed)
 
 != chrome://reftest/content/xul/resizer-bottomend.xhtml chrome://reftest/content/xul/blank-window.xhtml
 == chrome://reftest/content/xul/resizer-bottomend.xhtml chrome://reftest/content/xul/resizer-bottomright.xhtml
 != chrome://reftest/content/xul/resizer-bottomend.xhtml chrome://reftest/content/xul/resizer-bottomend-rtl.xhtml
diff --git a/layout/reftests/xul/tree-scrollbar-height-change-ref.xhtml b/layout/reftests/xul/tree-scrollbar-height-change-ref.xhtml
new file mode 100644
--- /dev/null
+++ b/layout/reftests/xul/tree-scrollbar-height-change-ref.xhtml
@@ -0,0 +1,32 @@
+<?xml version="1.0"?>
+<?xml-stylesheet href="chrome://global/skin" type="text/css"?>
+
+<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        xmlns:html="http://www.w3.org/1999/xhtml">
+
+  <tree seltype="single" rows="5">
+    <treecols>
+      <treecol flex="1"/>
+      <treecol flex="1"/>
+    </treecols>
+    <treechildren>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+    </treechildren>
+  </tree>
+</window>
diff --git a/layout/reftests/xul/tree-scrollbar-height-change.xhtml b/layout/reftests/xul/tree-scrollbar-height-change.xhtml
new file mode 100644
--- /dev/null
+++ b/layout/reftests/xul/tree-scrollbar-height-change.xhtml
@@ -0,0 +1,39 @@
+<?xml version="1.0"?>
+<?xml-stylesheet href="chrome://global/skin" type="text/css"?>
+
+<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        xmlns:html="http://www.w3.org/1999/xhtml">
+
+  <tree id="tree" seltype="single" rows="5" style="min-height: 3000px">
+    <treecols>
+      <treecol flex="1"/>
+      <treecol flex="1"/>
+    </treecols>
+    <treechildren>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+      <treeitem><treerow><treecell label="One"/><treecell label="Two"/></treerow></treeitem>
+    </treechildren>
+  </tree>
+<script>
+<![CDATA[
+  let tree = document.getElementById("tree");
+  tree.getBoundingClientRect();
+  tree.style.minHeight = "";
+]]>
+</script>
+</window>
diff --git a/layout/xul/tree/nsTreeBodyFrame.h b/layout/xul/tree/nsTreeBodyFrame.h
--- a/layout/xul/tree/nsTreeBodyFrame.h
+++ b/layout/xul/tree/nsTreeBodyFrame.h
@@ -114,11 +114,11 @@
   nsresult ClearStyleAndImageCaches();
   void RemoveImageCacheEntry(int32_t aRowIndex, nsTreeColumn* aCol);
 
   void CancelImageRequests();
 
-  void ManageReflowCallback(const nsRect& aRect, nscoord aHorzWidth);
+  void ManageReflowCallback();
 
   void DidReflow(nsPresContext*, const ReflowInput*) override;
 
   // nsIReflowCallback
   bool ReflowFinished() override;
@@ -566,10 +566,13 @@
   nscoord mHorzWidth;
   // The amount by which to adjust the width of the last cell.
   // This depends on whether or not the columnpicker and scrollbars are present.
   nscoord mAdjustWidth;
 
+  // Our last reflowed rect, used for invalidation, see ManageReflowCallback().
+  Maybe<nsRect> mLastReflowRect;
+
   // Cached heights and indent info.
   nsRect mInnerBox;  // 4-byte aligned
   int32_t mRowHeight;
   int32_t mIndentation;
 
diff --git a/layout/xul/tree/nsTreeBodyFrame.cpp b/layout/xul/tree/nsTreeBodyFrame.cpp
--- a/layout/xul/tree/nsTreeBodyFrame.cpp
+++ b/layout/xul/tree/nsTreeBodyFrame.cpp
@@ -363,34 +363,37 @@
   // XXX is this optimal if we haven't laid out yet?
   ScrollToRow(rowIndex);
   NS_ENSURE_TRUE_VOID(weakFrame.IsAlive());
 }
 
-void nsTreeBodyFrame::ManageReflowCallback(const nsRect& aRect,
-                                           nscoord aHorzWidth) {
-  if (!mReflowCallbackPosted &&
-      (!aRect.IsEqualEdges(mRect) || mHorzWidth != aHorzWidth)) {
-    PresShell()->PostReflowCallback(this);
-    mReflowCallbackPosted = true;
-    mOriginalHorzWidth = mHorzWidth;
-  } else if (mReflowCallbackPosted && mHorzWidth != aHorzWidth &&
-             mOriginalHorzWidth == aHorzWidth) {
+void nsTreeBodyFrame::ManageReflowCallback() {
+  const nscoord horzWidth = CalcHorzWidth(GetScrollParts());
+  if (!mReflowCallbackPosted) {
+    if (!mLastReflowRect || !mLastReflowRect->IsEqualEdges(mRect) ||
+        mHorzWidth != horzWidth) {
+      PresShell()->PostReflowCallback(this);
+      mReflowCallbackPosted = true;
+      mOriginalHorzWidth = mHorzWidth;
+    }
+  } else if (mHorzWidth != horzWidth && mOriginalHorzWidth == horzWidth) {
+    // FIXME(emilio): This doesn't seem sound to me, if the rect changes in the
+    // block axis.
     PresShell()->CancelReflowCallback(this);
     mReflowCallbackPosted = false;
     mOriginalHorzWidth = -1;
   }
+  mLastReflowRect = Some(mRect);
+  mHorzWidth = horzWidth;
 }
 
 nscoord nsTreeBodyFrame::GetIntrinsicBSize() {
   return mHasFixedRowCount ? mRowHeight * mPageLength : 0;
 }
 
 void nsTreeBodyFrame::DidReflow(nsPresContext* aPresContext,
                                 const ReflowInput* aReflowInput) {
-  nscoord horzWidth = CalcHorzWidth(GetScrollParts());
-  ManageReflowCallback(GetRect(), horzWidth);
-  mHorzWidth = horzWidth;
+  ManageReflowCallback();
   SimpleXULLeafFrame::DidReflow(aPresContext, aReflowInput);
 }
 
 bool nsTreeBodyFrame::ReflowFinished() {
   if (!mView) {