diff --git a/dom/base/ContentIterator.cpp b/dom/base/ContentIterator.cpp
index 48ca0fb24e95..dbcb4627e260 100644
--- a/dom/base/ContentIterator.cpp
+++ b/dom/base/ContentIterator.cpp
@@ -134,8 +134,7 @@ void ImplCycleCollectionUnlink(ContentIteratorBase& aField) {
   ImplCycleCollectionUnlink(aField.mClosestCommonInclusiveAncestor);
 }
 
-ContentIteratorBase::ContentIteratorBase(Order aOrder)
-    : mIsDone(false), mOrder(aOrder) {}
+ContentIteratorBase::ContentIteratorBase(Order aOrder) : mOrder(aOrder) {}
 
 ContentIteratorBase::~ContentIteratorBase() = default;
 
@@ -148,8 +147,6 @@ nsresult ContentIteratorBase::Init(nsINode* aRoot) {
     return NS_ERROR_NULL_POINTER;
   }
 
-  mIsDone = false;
-
   if (mOrder == Order::Pre) {
     mFirst = aRoot;
     mLast = ContentIteratorBase::GetDeepLastChild(aRoot);
@@ -166,8 +163,6 @@ nsresult ContentIteratorBase::Init(nsINode* aRoot) {
 }
 
 nsresult ContentIteratorBase::Init(nsRange* aRange) {
-  mIsDone = false;
-
   if (NS_WARN_IF(!aRange)) {
     return NS_ERROR_INVALID_ARG;
   }
@@ -183,8 +178,6 @@ nsresult ContentIteratorBase::Init(nsINode* aStartContainer,
                                    uint32_t aStartOffset,
                                    nsINode* aEndContainer,
                                    uint32_t aEndOffset) {
-  mIsDone = false;
-
   if (NS_WARN_IF(!RangeUtils::IsValidPoints(aStartContainer, aStartOffset,
                                             aEndContainer, aEndOffset))) {
     return NS_ERROR_INVALID_ARG;
@@ -196,8 +189,6 @@ nsresult ContentIteratorBase::Init(nsINode* aStartContainer,
 
 nsresult ContentIteratorBase::Init(const RawRangeBoundary& aStart,
                                    const RawRangeBoundary& aEnd) {
-  mIsDone = false;
-
   if (NS_WARN_IF(!RangeUtils::IsValidPoints(aStart, aEnd))) {
     return NS_ERROR_INVALID_ARG;
   }
@@ -293,12 +284,10 @@ nsresult ContentIteratorBase::Initializer::Run() {
 
   // If either first or last is null, they both have to be null!
   if (!mIterator.mFirst || !mIterator.mLast) {
-    mIterator.mFirst = nullptr;
-    mIterator.mLast = nullptr;
+    mIterator.SetEmpty();
   }
 
   mIterator.mCurNode = mIterator.mFirst;
-  mIterator.mIsDone = !mIterator.mCurNode;
 
   return NS_OK;
 }
@@ -460,7 +449,6 @@ void ContentIteratorBase::SetEmpty() {
   mFirst = nullptr;
   mLast = nullptr;
   mClosestCommonInclusiveAncestor = nullptr;
-  mIsDone = true;
 }
 
 // static
@@ -585,12 +573,11 @@ nsINode* ContentIteratorBase::NextNode(nsINode* aNode) {
   nsINode* parent = node->GetParentNode();
   if (NS_WARN_IF(!parent)) {
     MOZ_ASSERT(parent, "The node is the root node but not the last node");
-    mIsDone = true;
+    mCurNode = nullptr;
     return node;
   }
 
-  nsIContent* sibling = node->GetNextSibling();
-  if (sibling) {
+  if (nsIContent* sibling = node->GetNextSibling()) {
     // next node is sibling's "deep left" child
     return ContentIteratorBase::GetDeepFirstChild(sibling);
   }
@@ -606,7 +593,7 @@ nsINode* ContentIteratorBase::PrevNode(nsINode* aNode) {
     nsINode* parent = node->GetParentNode();
     if (NS_WARN_IF(!parent)) {
       MOZ_ASSERT(parent, "The node is the root node but not the first node");
-      mIsDone = true;
+      mCurNode = nullptr;
       return aNode;
     }
 
@@ -632,35 +619,36 @@ nsINode* ContentIteratorBase::PrevNode(nsINode* aNode) {
  ******************************************************/
 
 void ContentIteratorBase::First() {
-  if (mFirst) {
-    mozilla::DebugOnly<nsresult> rv = PositionAt(mFirst);
-    NS_ASSERTION(NS_SUCCEEDED(rv), "Failed to position iterator!");
+  if (!mFirst) {
+    MOZ_ASSERT(IsDone());
+    mCurNode = nullptr;
+    return;
   }
 
-  mIsDone = mFirst == nullptr;
+  mozilla::DebugOnly<nsresult> rv = PositionAt(mFirst);
+  NS_ASSERTION(NS_SUCCEEDED(rv), "Failed to position iterator!");
 }
 
 void ContentIteratorBase::Last() {
   // Note that mLast can be nullptr if SetEmpty() is called in Init()
   // since at that time, Init() returns NS_OK.
   if (!mLast) {
-    MOZ_ASSERT(mIsDone);
+    MOZ_ASSERT(IsDone());
+    mCurNode = nullptr;
     return;
   }
 
   mozilla::DebugOnly<nsresult> rv = PositionAt(mLast);
   NS_ASSERTION(NS_SUCCEEDED(rv), "Failed to position iterator!");
-
-  mIsDone = mLast == nullptr;
 }
 
 void ContentIteratorBase::Next() {
-  if (mIsDone || NS_WARN_IF(!mCurNode)) {
+  if (IsDone()) {
     return;
   }
 
   if (mCurNode == mLast) {
-    mIsDone = true;
+    mCurNode = nullptr;
     return;
   }
 
@@ -668,20 +656,18 @@ void ContentIteratorBase::Next() {
 }
 
 void ContentIteratorBase::Prev() {
-  if (NS_WARN_IF(mIsDone) || NS_WARN_IF(!mCurNode)) {
+  if (IsDone()) {
     return;
   }
 
   if (mCurNode == mFirst) {
-    mIsDone = true;
+    mCurNode = nullptr;
     return;
   }
 
   mCurNode = PrevNode(mCurNode);
 }
 
-bool ContentIteratorBase::IsDone() { return mIsDone; }
-
 // Keeping arrays of indexes for the stack of nodes makes PositionAt
 // interesting...
 nsresult ContentIteratorBase::PositionAt(nsINode* aCurNode) {
@@ -691,7 +677,6 @@ nsresult ContentIteratorBase::PositionAt(nsINode* aCurNode) {
 
   // take an early out if this doesn't actually change the position
   if (mCurNode == aCurNode) {
-    mIsDone = false;
     return NS_OK;
   }
   mCurNode = aCurNode;
@@ -735,24 +720,13 @@ nsresult ContentIteratorBase::PositionAt(nsINode* aCurNode) {
       (NS_WARN_IF(!first.IsSet()) || NS_WARN_IF(!last.IsSet()) ||
        NS_WARN_IF(!NodeIsInTraversalRange(mCurNode, mOrder == Order::Pre, first,
                                           last)))) {
-    mIsDone = true;
+    mCurNode = nullptr;
     return NS_ERROR_FAILURE;
   }
 
-  mIsDone = false;
   return NS_OK;
 }
 
-nsINode* ContentIteratorBase::GetCurrentNode() {
-  if (mIsDone) {
-    return nullptr;
-  }
-
-  NS_ASSERTION(mCurNode, "Null current node in an iterator that's not done!");
-
-  return mCurNode;
-}
-
 /******************************************************
  * ContentSubtreeIterator init routines
  ******************************************************/
@@ -764,8 +738,6 @@ nsresult ContentSubtreeIterator::Init(nsINode* aRoot) {
 nsresult ContentSubtreeIterator::Init(nsRange* aRange) {
   MOZ_ASSERT(aRange);
 
-  mIsDone = false;
-
   if (NS_WARN_IF(!aRange->IsPositioned())) {
     return NS_ERROR_INVALID_ARG;
   }
@@ -785,8 +757,6 @@ nsresult ContentSubtreeIterator::Init(nsINode* aStartContainer,
 
 nsresult ContentSubtreeIterator::Init(const RawRangeBoundary& aStartBoundary,
                                       const RawRangeBoundary& aEndBoundary) {
-  mIsDone = false;
-
   RefPtr<nsRange> range =
       nsRange::Create(aStartBoundary, aEndBoundary, IgnoreErrors());
   if (NS_WARN_IF(!range) || NS_WARN_IF(!range->IsPositioned())) {
@@ -972,26 +942,18 @@ nsIContent* ContentSubtreeIterator::DetermineLastContent() const {
  ****************************************************************/
 
 // we can't call PositionAt in a subtree iterator...
-void ContentSubtreeIterator::First() {
-  mIsDone = mFirst == nullptr;
-
-  mCurNode = mFirst;
-}
+void ContentSubtreeIterator::First() { mCurNode = mFirst; }
 
 // we can't call PositionAt in a subtree iterator...
-void ContentSubtreeIterator::Last() {
-  mIsDone = mLast == nullptr;
-
-  mCurNode = mLast;
-}
+void ContentSubtreeIterator::Last() { mCurNode = mLast; }
 
 void ContentSubtreeIterator::Next() {
-  if (mIsDone || !mCurNode) {
+  if (IsDone()) {
     return;
   }
 
   if (mCurNode == mLast) {
-    mIsDone = true;
+    mCurNode = nullptr;
     return;
   }
 
@@ -1013,22 +975,17 @@ void ContentSubtreeIterator::Next() {
   }
 
   mCurNode = nextNode;
-
-  // This shouldn't be needed, but since our selection code can put us
-  // in a situation where mLast is in generated content, we need this
-  // to stop the iterator when we've walked past past the last node!
-  mIsDone = mCurNode == nullptr;
 }
 
 void ContentSubtreeIterator::Prev() {
   // Prev should be optimized to use the mStartNodes, just as Next
   // uses mInclusiveAncestorsOfEndContainer.
-  if (mIsDone || !mCurNode) {
+  if (IsDone()) {
     return;
   }
 
   if (mCurNode == mFirst) {
-    mIsDone = true;
+    mCurNode = nullptr;
     return;
   }
 
@@ -1041,16 +998,10 @@ void ContentSubtreeIterator::Prev() {
   prevNode = ContentIteratorBase::GetDeepLastChild(prevNode);
 
   mCurNode = GetTopAncestorInRange(prevNode);
-
-  // This shouldn't be needed, but since our selection code can put us
-  // in a situation where mFirst is in generated content, we need this
-  // to stop the iterator when we've walked past past the first node!
-  mIsDone = mCurNode == nullptr;
 }
 
 nsresult ContentSubtreeIterator::PositionAt(nsINode* aCurNode) {
   NS_ERROR("Not implemented!");
-
   return NS_ERROR_NOT_IMPLEMENTED;
 }
 
diff --git a/dom/base/ContentIterator.h b/dom/base/ContentIterator.h
index adba24d6339c..012443c8dd36 100644
--- a/dom/base/ContentIterator.h
+++ b/dom/base/ContentIterator.h
@@ -51,9 +51,9 @@ class ContentIteratorBase {
   virtual void Next();
   virtual void Prev();
 
-  virtual nsINode* GetCurrentNode();
+  nsINode* GetCurrentNode() const { return mCurNode; }
 
-  virtual bool IsDone();
+  bool IsDone() const { return !mCurNode; }
 
   virtual nsresult PositionAt(nsINode* aCurNode);
 
@@ -102,8 +102,6 @@ class ContentIteratorBase {
   // See <https://dom.spec.whatwg.org/#concept-tree-inclusive-ancestor>.
   nsCOMPtr<nsINode> mClosestCommonInclusiveAncestor;
 
-  bool mIsDone;
-
   const Order mOrder;
 
   friend void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback&,
@@ -185,14 +183,14 @@ class ContentSubtreeIterator final : public ContentIteratorBase {
   virtual nsresult Init(const RawRangeBoundary& aStartBoundary,
                         const RawRangeBoundary& aEndBoundary) override;
 
-  virtual void Next() override;
-  virtual void Prev() override;
+  void Next() override;
+  void Prev() override;
   // Must override these because we don't do PositionAt
-  virtual void First() override;
+  void First() override;
   // Must override these because we don't do PositionAt
-  virtual void Last() override;
+  void Last() override;
 
-  virtual nsresult PositionAt(nsINode* aCurNode) override;
+  nsresult PositionAt(nsINode* aCurNode) override;
 
   friend void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback&,
                                           ContentSubtreeIterator&, const char*,
diff --git a/testing/web-platform/tests/selection/drag-disabled-textarea-shadow-dom.html b/testing/web-platform/tests/selection/drag-disabled-textarea-shadow-dom.html
new file mode 100644
index 000000000000..9270cfc5c6be
--- /dev/null
+++ b/testing/web-platform/tests/selection/drag-disabled-textarea-shadow-dom.html
@@ -0,0 +1,39 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<!-- Conceptually this is just a crashtest, but we need testharness.js so that testdriver works as expected, see https://github.com/web-platform-tests/wpt/issues/31739 -->
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<link rel=help href="https://bugzilla.mozilla.org/show_bug.cgi?id=1739079">
+<span id="outer"></span>
+<script>
+  const t = async_test("Shouldn't crash when dragging disabled textarea in shadow dom");
+  const outer = document.getElementById("outer");
+  outer.attachShadow({ mode: "open" }).innerHTML = `
+    <span id="inner" style="pointer-events: none">
+      <textarea disabled></textarea>
+    </span>
+  `;
+  const inner = outer.shadowRoot.getElementById("inner");
+  inner.attachShadow({ mode: "open" }).innerHTML = `
+    <div style="display: flex">
+      <slot></slot>
+    </div>
+  `;
+  const textarea = outer.shadowRoot.querySelector("textarea");
+  window.addEventListener("load", t.step_func(function() {
+    const rect = textarea.getBoundingClientRect();
+    new test_driver.Actions()
+        .pointerMove(rect.left + 5, rect.top + 5)
+        .pointerDown()
+        .pointerMove(rect.left, + 50, rect.top + 50)
+        .pointerMove(0, 0)
+        .pointerUp()
+        .send()
+        .then(t.step_func_done(function() {
+          assert_true(true, "Didn't crash nor hang");
+        }));
+  }));
+</script>