diff --git a/dom/base/Document.cpp b/dom/base/Document.cpp
index 450e83209fb2..f1a0cdc52070 100644
--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -5392,8 +5392,7 @@ bool Document::ExecCommand(const nsAString& aHTMLCommandName, bool aShowUI,
 
   // If we're running an execCommand, we should just return false.
   // https://github.com/w3c/editing/issues/200#issuecomment-575241816
-  if (!StaticPrefs::dom_document_exec_command_nested_calls_allowed() &&
-      !markRunningExecCommand.IsSafeToRun()) {
+  if (!markRunningExecCommand.IsSafeToRun()) {
     return false;
   }
 
diff --git a/editor/libeditor/crashtests/1402904.html b/editor/libeditor/crashtests/1402904.html
deleted file mode 100644
index 544d01208ae2..000000000000
--- a/editor/libeditor/crashtests/1402904.html
+++ /dev/null
@@ -1,38 +0,0 @@
-<script>
-function onLoad() {
-  // For emulating the traditional behavior, collapse Selection to end of the
-  // parent of <embed> (<embed> is not a container, therefore, its parent is the
-  // deepest last child container element of the <body>).
-  getSelection().collapse(
-    document.querySelector("embed").parentElement,
-    document.querySelector("embed").parentElement.childNodes.length
-  ); // Point the <embed>
-  const option = document.querySelector("option");
-  option.addEventListener("click", () => {
-    document.execCommand("forwardDelete");
-  });
-  const li2 = document.getElementById("li2");
-  li2.addEventListener("DOMNodeInserted", () => {
-    option.click();
-  });
-  const select = document.querySelector("select");
-  select.parentElement.setAttribute("onpageshow", "onPageShow()");
-}
-
-function onPageShow() {
-  const li1 = document.getElementById("li1");
-  li1.addEventListener("DOMSubtreeModified", () => {
-    document.execCommand("selectAll");
-    document.execCommand("indent");
-  });
-  li1.appendChild(document.createElement("legend"));
-}
-</script>
-<body onload="onLoad()">
-<select>
-<option></option>
-</select>
-<li id="li1"></li>
-<ul contenteditable="true">
-<li id="li2"></li>
-<embed>a;#2
diff --git a/editor/libeditor/crashtests/1405747.html b/editor/libeditor/crashtests/1405747.html
deleted file mode 100644
index dae3a130f0da..000000000000
--- a/editor/libeditor/crashtests/1405747.html
+++ /dev/null
@@ -1,40 +0,0 @@
-<script>
-let th;
-function onLoad() {
-  // For emulating the traditional behavior, collapse Selection to end of the
-  // <colgroup> which is the last child of the <body>.
-  getSelection().collapse(
-    document.querySelector("colgroup"),
-    document.querySelector("colgroup").childNodes.length
-  );
-  th = document.querySelector("th"); // Cache the target for removing the event handler.
-  try {
-    th.addEventListener("DOMSubtreeModified", onDOMSubtreeModified);
-  } catch(e) {}
-  try {
-    th.align = "";
-  } catch(e) {}
-}
-
-let count = 0;
-function onDOMSubtreeModified() {
-  if (count++ == 1) {
-    // If we didn't stop testing this, this event handler would be called too
-    // many times.  It's enough to run twice to reproduce the bug report.
-    th.removeEventListener("DOMSubtreeModified", onDOMSubtreeModified);
-  }
-  try {
-    document.execCommand("selectAll");
-  } catch(e) {}
-  try {
-    document.execCommand("justifyCenter");
-  } catch(e) {}
-  try {
-    document.execCommand("forwardDelete");
-  } catch(e) {}
-}
-</script>
-<body onload="onLoad()">
-<table contenteditable>
-<th></th>
-<colgroup></body>
diff --git a/editor/libeditor/crashtests/1464251.html b/editor/libeditor/crashtests/1464251.html
deleted file mode 100644
index afe7e875610c..000000000000
--- a/editor/libeditor/crashtests/1464251.html
+++ /dev/null
@@ -1,25 +0,0 @@
-<script>
-var count = 0;
-function onLoad() {
-  // For emulating the traditional behavior, collapse Selection to end of the
-  // text node in the <s> which is the deepest last child (and a container) of
-  // the <body> (i.e., end of the the text node after the last comment node).
-  const s = document.querySelector("s");
-  getSelection().collapse(s.lastChild, s.lastChild.length);
-  document.execCommand("delete");
-}
-
-function onInputOrDOMNodeInserted() {
-  if (++count >= 3) {
-    return;
-  }
-  addEventListener("DOMNodeInserted", onInputOrDOMNodeInserted);
-  document.execCommand("removeFormat");
-  document.execCommand("insertText", false, "1");
-}
-</script>
-<body onload="onLoad()">
-<ol oninput="onInputOrDOMNodeInserted()" contenteditable>
-<!-- x -->
-<s>
-<!-- x -->
diff --git a/editor/libeditor/crashtests/1474978.html b/editor/libeditor/crashtests/1474978.html
deleted file mode 100644
index d7eb01e03b29..000000000000
--- a/editor/libeditor/crashtests/1474978.html
+++ /dev/null
@@ -1,21 +0,0 @@
-<script>
-function onLoad() {
-  const dd = document.querySelector("dd[contenteditable]");
-  // For emulating the traditional behavior, collapse Selection to end of the
-  // text node at end of the <dd contenteditable> which is the deepest last
-  // child of the <body> (end of the text node after the <template>).
-  getSelection().collapse(dd.lastChild, dd.lastChild.length);
-  getSelection().setPosition(
-    document.querySelector("template")
-  );
-  dd.addEventListener("DOMNodeInserted", () => {
-    document.execCommand("selectAll");
-    document.execCommand("insertText", false, "");
-  });
-  document.execCommand("insertImage", false, "#");
-}
-</script>
-<body onload="onLoad()">
-<dd contenteditable>
-<template></template>
-</dd></body>
diff --git a/editor/libeditor/crashtests/1666556.html b/editor/libeditor/crashtests/1666556.html
deleted file mode 100644
index 8c8c18574ad5..000000000000
--- a/editor/libeditor/crashtests/1666556.html
+++ /dev/null
@@ -1,28 +0,0 @@
-<script>
-function onError() {
-  document.querySelector("details").appendChild(
-    document.querySelector("p")
-  );
-  document.execCommand("indent");
-}
-
-function onLoadOfStyle() {
-  document.execCommand("delete");
-  document.querySelector("details").contentEditable = "true";
-  // For emulating the traditional behavior, collapse Selection to end of the
-  // text node at end of the <style> (end of the text node after the comment
-  // node).
-  const style = document.querySelector("style");
-  getSelection().collapse(style.lastChild, style.lastChild.length);
-  document.querySelector("input").select();
-}
-</script>
-<video focus="false">
-<source onerror="onError()">
-</video>
-<details open>
-<p>
-<input contenteditable="false">
-<style onload="onLoadOfStyle()">
-<!-- x -->
-</style></p></details></body>
diff --git a/editor/libeditor/crashtests/crashtests.list b/editor/libeditor/crashtests/crashtests.list
index bc9b7a3f2d3f..515d278a1453 100644
--- a/editor/libeditor/crashtests/crashtests.list
+++ b/editor/libeditor/crashtests/crashtests.list
@@ -58,8 +58,6 @@ load 1393171.html
 needs-focus load 1402196.html
 load 1402469.html
 load 1402526.html
-pref(dom.document.exec_command.nested_calls_allowed,true) asserts(1) load 1402904.html # assertion is that mutation event listener caused by execCommand calls another execCommand
-pref(dom.document.exec_command.nested_calls_allowed,true) asserts(1) load 1405747.html # assertion is that mutation event listener caused by execCommand calls another execCommand
 load 1405897.html
 load 1408170.html
 asserts(0-1) load 1414581.html
@@ -75,9 +73,7 @@ load 1441619.html
 load 1443664.html
 skip-if(Android) needs-focus load 1444630.html
 load 1446451.html
-pref(dom.document.exec_command.nested_calls_allowed,true) load 1464251.html
 pref(layout.accessiblecaret.enabled,true) load 1470926.html
-pref(dom.document.exec_command.nested_calls_allowed,true) asserts(2) load 1474978.html # assertion is that mutation event listener caused by execCommand calls another execCommand
 load 1517028.html
 load 1525481.html
 load 1533913.html
@@ -109,7 +105,6 @@ load 1659717.html
 load 1663725.html # throws
 load 1655508.html
 load 1655988.html
-pref(dom.document.exec_command.nested_calls_allowed,true) load 1666556.html
 load 1677566.html
 load 1691051.html
 load 1699866.html
diff --git a/editor/libeditor/tests/mochitest.toml b/editor/libeditor/tests/mochitest.toml
index 15a6d4c37990..7d68fc7e0b85 100644
--- a/editor/libeditor/tests/mochitest.toml
+++ b/editor/libeditor/tests/mochitest.toml
@@ -381,8 +381,6 @@ skip-if = ["headless"]
 
 ["test_bug1409520.html"]
 
-["test_bug1425997.html"]
-
 ["test_bug1543312.html"]
 
 ["test_bug1568996.html"]
diff --git a/editor/libeditor/tests/test_bug1425997.html b/editor/libeditor/tests/test_bug1425997.html
deleted file mode 100644
index 637d77a0caaf..000000000000
--- a/editor/libeditor/tests/test_bug1425997.html
+++ /dev/null
@@ -1,63 +0,0 @@
-<!DOCTYPE html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=1425997
--->
-<html>
-<head>
-  <title>Test for Bug 1425997</title>
-  <script src="/tests/SimpleTest/SimpleTest.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
-</head>
-<body>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1425997">Mozilla Bug 1425997</a>
-<p id="display"></p>
-<div id="content" style="display: none;">
-
-</div>
-
-<div id="editor" contenteditable>
-<!-- -->
-<span id="inline">foo</span>
-</div>
-
-<pre id="test">
-
-<script class="testbody" type="application/javascript">
-SimpleTest.waitForExplicitFinish();
-// 2 assertions are recorded due to nested execCommand() but not a problem.
-// They are necessary to detect invalid method call without mutation event listers.
-SimpleTest.expectAssertions(2, 2);
-SimpleTest.waitForFocus(async function() {
-  await SpecialPowers.pushPrefEnv({set: [["dom.document.exec_command.nested_calls_allowed", true]]});
-  let selection = window.getSelection();
-  let editor = document.getElementById("editor");
-  function onCharacterDataModified() {
-    // Until removing all NBSPs which were inserted by the editor,
-    // emulates Backspace key with "delete" command.
-    // When this test is created, the behavior was:
-    //   after 1st delete: "\n<!-- -->&nbsp;\n"
-    //   after 2nd delete: "\n<!-- -->&nbsp;"
-    //   Then, selection is moved into the comment node and deletion won't
-    //   work after that.
-    while (editor.innerHTML.includes("&nbsp;")) {
-      let preInnerHTML = editor.innerHTML;
-      if (!document.execCommand("delete", false) || preInnerHTML === editor.innerHTML) {
-        break;
-      }
-      info(`editor.innerHTML: "${editor.innerHTML.replace(/\n/g, "\\n")}"`);
-    }
-  }
-  editor.addEventListener("DOMCharacterDataModified", onCharacterDataModified, { once: true });
-  editor.focus();
-  selection.selectAllChildren(document.getElementById("inline"));
-  document.execCommand("insertHTML", false, "text");
-  // This expected result is just same as the result of Chrome.
-  // If the spec says this is wrong, feel free to change this result.
-  todo_is(editor.innerHTML, "\n<!-- --><span id=\"inline\">text</span>",
-          "The 'foo' should be replaced with 'text' and whitespaces before the span element should be removed");
-  SimpleTest.finish();
-});
-</script>
-</pre>
-</body>
-</html>
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index 09b1be36a8c6..0da008fc9e22 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -2378,13 +2378,6 @@
   value: @IS_NOT_EARLY_BETA_OR_EARLIER@
   mirror: always
 
-# If set this to true, `Document.execCommand` may be performed nestedly.
-# Otherwise, nested calls just return false.
-- name: dom.document.exec_command.nested_calls_allowed
-  type: bool
-  value: false
-  mirror: always
-
 # Only intended for fuzzing purposes, this will break mozPrintCallback, etc.
 - name: dom.window_print.fuzzing.block_while_printing
   type: bool
diff --git a/testing/web-platform/meta/editing/crashtests/backcolor-in-nested-editing-host-td-from-DOMAttrModified.html.ini b/testing/web-platform/meta/editing/crashtests/backcolor-in-nested-editing-host-td-from-DOMAttrModified.html.ini
deleted file mode 100644
index b1a9871dda64..000000000000
--- a/testing/web-platform/meta/editing/crashtests/backcolor-in-nested-editing-host-td-from-DOMAttrModified.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[backcolor-in-nested-editing-host-td-from-DOMAttrModified.html]
-  prefs: [dom.document.exec_command.nested_calls_allowed:true]
