diff --git a/build/tasks/esbuild.js b/build/tasks/esbuild.js
index 6a5479dff9..30dbeb4ef6 100644
--- a/build/tasks/esbuild.js
+++ b/build/tasks/esbuild.js
@@ -26,7 +26,10 @@ module.exports = function (grunt) {
             bundle: true
           })
             .then(done)
-            .catch(done);
+            .catch(e => {
+              grunt.fail.fatal(e);
+              done();
+            });
         });
       });
     }
diff --git a/lib/checks/navigation/region-evaluate.js b/lib/checks/navigation/region-evaluate.js
index 0fed9ea4b3..0e14b8a168 100644
--- a/lib/checks/navigation/region-evaluate.js
+++ b/lib/checks/navigation/region-evaluate.js
@@ -4,7 +4,6 @@ import * as standards from '../../commons/standards';
 import matches from '../../commons/matches';
 import cache from '../../core/base/cache';
 
-const landmarkRoles = standards.getAriaRolesByType('landmark');
 const implicitAriaLiveRoles = ['alert', 'log', 'status'];
 
 export default function regionEvaluate(node, options, virtualNode) {
@@ -92,6 +91,7 @@ function isRegion(virtualNode, options) {
   const node = virtualNode.actualNode;
   const role = getRole(virtualNode);
   const ariaLive = (node.getAttribute('aria-live') || '').toLowerCase().trim();
+  const landmarkRoles = standards.getAriaRolesByType('landmark');
 
   // Ignore content inside of aria-live
   if (
diff --git a/lib/commons/color/incomplete-data.js b/lib/commons/color/incomplete-data.js
index 0ece568087..c9b7194f32 100644
--- a/lib/commons/color/incomplete-data.js
+++ b/lib/commons/color/incomplete-data.js
@@ -1,9 +1,12 @@
+import cache from '../../core/base/cache';
+
+const cacheKey = 'color.incompleteData';
+
 /**
  * API for handling incomplete color data
  * @namespace axe.commons.color.incompleteData
  * @inner
  */
-let data = {};
 const incompleteData = {
   /**
    * Store incomplete data by key with a string value
@@ -17,6 +20,7 @@ const incompleteData = {
     if (typeof key !== 'string') {
       throw new Error('Incomplete data: key must be a string');
     }
+    const data = cache.get(cacheKey, () => ({}));
     if (reason) {
       data[key] = reason;
     }
@@ -31,7 +35,8 @@ const incompleteData = {
    * @return {String} String for reason we couldn't tell
    */
   get: function (key) {
-    return data[key];
+    const data = cache.get(cacheKey);
+    return data?.[key];
   },
   /**
    * Clear incomplete data on demand
@@ -40,7 +45,7 @@ const incompleteData = {
    * @instance
    */
   clear: function () {
-    data = {};
+    cache.set(cacheKey, {});
   }
 };
 
diff --git a/lib/commons/standards/implicit-html-roles.js b/lib/commons/standards/implicit-html-roles.js
index 0a7b2da142..cc3c8edb74 100644
--- a/lib/commons/standards/implicit-html-roles.js
+++ b/lib/commons/standards/implicit-html-roles.js
@@ -10,13 +10,19 @@ import isRowHeader from '../table/is-row-header';
 import sanitize from '../text/sanitize';
 import isFocusable from '../dom/is-focusable';
 import { closest } from '../../core/utils';
+import cache from '../../core/base/cache';
 import getExplicitRole from '../aria/get-explicit-role';
 
-const sectioningElementSelector =
-  getElementsByContentType('sectioning')
-    .map(nodeName => `${nodeName}:not([role])`)
-    .join(', ') +
-  ' , main:not([role]), [role=article], [role=complementary], [role=main], [role=navigation], [role=region]';
+const getSectioningElementSelector = () => {
+  return cache.get('sectioningElementSelector', () => {
+    return (
+      getElementsByContentType('sectioning')
+        .map(nodeName => `${nodeName}:not([role])`)
+        .join(', ') +
+      ' , main:not([role]), [role=article], [role=complementary], [role=main], [role=navigation], [role=region]'
+    );
+  });
+};
 
 // sectioning elements only have an accessible name if the
 // aria-label, aria-labelledby, or title attribute has valid
@@ -64,7 +70,7 @@ const implicitHtmlRoles = {
   fieldset: 'group',
   figure: 'figure',
   footer: vNode => {
-    const sectioningElement = closest(vNode, sectioningElementSelector);
+    const sectioningElement = closest(vNode, getSectioningElementSelector());
 
     return !sectioningElement ? 'contentinfo' : null;
   },
@@ -78,7 +84,7 @@ const implicitHtmlRoles = {
   h5: 'heading',
   h6: 'heading',
   header: vNode => {
-    const sectioningElement = closest(vNode, sectioningElementSelector);
+    const sectioningElement = closest(vNode, getSectioningElementSelector());
 
     return !sectioningElement ? 'banner' : null;
   },
diff --git a/lib/core/base/virtual-node/virtual-node.js b/lib/core/base/virtual-node/virtual-node.js
index e752e07040..589b61237f 100644
--- a/lib/core/base/virtual-node/virtual-node.js
+++ b/lib/core/base/virtual-node/virtual-node.js
@@ -3,7 +3,6 @@ import { isXHTML, validInputTypes } from '../../utils';
 import { isFocusable, getTabbableElements } from '../../../commons/dom';
 import cache from '../cache';
 
-let isXHTMLGlobal;
 let nodeIndex = 0;
 
 class VirtualNode extends AbstractVirtualNode {
@@ -27,11 +26,7 @@ class VirtualNode extends AbstractVirtualNode {
 
     this._isHidden = null; // will be populated by axe.utils.isHidden
     this._cache = {};
-
-    if (typeof isXHTMLGlobal === 'undefined') {
-      isXHTMLGlobal = isXHTML(node.ownerDocument);
-    }
-    this._isXHTML = isXHTMLGlobal;
+    this._isXHTML = isXHTML(node.ownerDocument);
 
     // we will normalize the type prop for inputs by looking strictly
     // at the attribute and not what the browser resolves the type
diff --git a/lib/core/utils/frame-messenger/message-id.js b/lib/core/utils/frame-messenger/message-id.js
index 0766e1b36d..d01533ca7e 100644
--- a/lib/core/utils/frame-messenger/message-id.js
+++ b/lib/core/utils/frame-messenger/message-id.js
@@ -1,5 +1,6 @@
 import { v4 as createUuid } from '../uuid';
 
+// No cache, so that this can persist across axe.run calls
 const messageIds = [];
 
 export function createMessageId() {
diff --git a/lib/core/utils/frame-messenger/post-message.js b/lib/core/utils/frame-messenger/post-message.js
index 5f90b76ca3..a682bee5d1 100644
--- a/lib/core/utils/frame-messenger/post-message.js
+++ b/lib/core/utils/frame-messenger/post-message.js
@@ -15,10 +15,6 @@ import { createMessageId } from './message-id';
  * @return {Boolean} true if the message was sent
  */
 export function postMessage(win, data, sendToParent, replyHandler) {
-  if (typeof replyHandler === 'function') {
-    storeReplyHandler(data.channelId, replyHandler, sendToParent);
-  }
-
   // Prevent messaging to an inappropriate window
   sendToParent ? assertIsParentWindow(win) : assertIsFrameWindow(win);
   if (data.message instanceof Error && !sendToParent) {
@@ -37,6 +33,9 @@ export function postMessage(win, data, sendToParent, replyHandler) {
     return false;
   }
 
+  if (typeof replyHandler === 'function') {
+    storeReplyHandler(data.channelId, replyHandler, sendToParent);
+  }
   // There is no way to know the origin of `win`, so we'll try them all.
   allowedOrigins.forEach(origin => {
     try {
diff --git a/lib/core/utils/get-selector.js b/lib/core/utils/get-selector.js
index 02c192f8ec..28af5bf6af 100644
--- a/lib/core/utils/get-selector.js
+++ b/lib/core/utils/get-selector.js
@@ -5,7 +5,6 @@ import matchesSelector from './element-matches';
 import isXHTML from './is-xhtml';
 import getShadowSelector from './get-shadow-selector';
 
-let xhtml;
 const ignoredAttributes = [
   'class',
   'style',
@@ -238,9 +237,7 @@ function getElmId(elm) {
  * @return {String|Array<String>}	Base CSS selector for the node
  */
 function getBaseSelector(elm) {
-  if (typeof xhtml === 'undefined') {
-    xhtml = isXHTML(document);
-  }
+  const xhtml = isXHTML(document);
   return escapeSelector(xhtml ? elm.localName : elm.nodeName.toLowerCase());
 }
 
diff --git a/lib/core/utils/is-xhtml.js b/lib/core/utils/is-xhtml.js
index 09851a2153..3ed4c51776 100644
--- a/lib/core/utils/is-xhtml.js
+++ b/lib/core/utils/is-xhtml.js
@@ -1,3 +1,5 @@
+import memoize from './memoize';
+
 /**
  * Determines if a document node is XHTML
  * @method isXHTML
@@ -5,11 +7,11 @@
  * @param {Node} doc a document node
  * @return {Boolean}
  */
-function isXHTML(doc) {
-  if (!doc.createElement) {
+const isXHTML = memoize(doc => {
+  if (!doc?.createElement) {
     return false;
   }
   return doc.createElement('A').localName === 'A';
-}
+});
 
 export default isXHTML;
diff --git a/lib/core/utils/query-selector-all-filter.js b/lib/core/utils/query-selector-all-filter.js
index 770e3651c1..d1d92461b3 100644
--- a/lib/core/utils/query-selector-all-filter.js
+++ b/lib/core/utils/query-selector-all-filter.js
@@ -1,3 +1,4 @@
+import cache from '../base/cache';
 import { matchesExpression, convertSelector } from './matches';
 import { getNodesMatchingExpression } from './selector-cache';
 
@@ -19,17 +20,20 @@ function createLocalVariables(
   return retVal;
 }
 
-/**
- * Allocating new objects in createLocalVariables is quite expensive given
- * that matchExpressions is in the hot path.
- *
- * Keep track of previously allocated objects to avoid useless allocations
- * and garbage collection. This is intentionally shared between calls of
- * matchExpressions.
- */
-const recycledLocalVariables = [];
-
 function matchExpressions(domTree, expressions, filter) {
+  /**
+   * Allocating new objects in createLocalVariables is quite expensive given
+   * that matchExpressions is in the hot path.
+   *
+   * Keep track of previously allocated objects to avoid useless allocations
+   * and garbage collection. This is intentionally shared between calls of
+   * matchExpressions.
+   */
+  const recycledLocalVariables = cache.get(
+    'qsa.recycledLocalVariables',
+    () => []
+  );
+
   const stack = [];
   const vNodes = Array.isArray(domTree) ? domTree : [domTree];
   let currentLevel = createLocalVariables(
diff --git a/test/checks/navigation/region.js b/test/checks/navigation/region.js
index 2c23ddc084..fb4d13b3e9 100644
--- a/test/checks/navigation/region.js
+++ b/test/checks/navigation/region.js
@@ -18,6 +18,7 @@ describe('region', function () {
   afterEach(function () {
     fixture.innerHTML = '';
     checkContext.reset();
+    axe.reset();
   });
 
   it('should return true when content is inside the region', function () {
@@ -28,6 +29,23 @@ describe('region', function () {
     assert.isTrue(checkEvaluate.apply(checkContext, checkArgs));
   });
 
+  it('should return true when a region role is added to standards', () => {
+    axe.configure({
+      standards: {
+        ariaRoles: {
+          feed: {
+            type: 'landmark'
+          }
+        }
+      }
+    });
+    var checkArgs = checkSetup(
+      '<div role="feed" id="target">This is random content.</div>' +
+        '<div role="main"><h1 id="mainheader">Introduction</h1></div>'
+    );
+    assert.isTrue(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
   it('should return false when img content is outside the region', function () {
     var checkArgs = checkSetup(
       '<img id="target" src="data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7"><div role="main"><h1 id="mainheader" tabindex="0">Introduction</h1></div>'