diff --git a/.eslintrc.js b/.eslintrc.js
index 0b53d7785a4a..b6d29da1ecdb 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -394,6 +394,8 @@ const base = {
   'unicorn/no-lonely-if': ERROR,
   // forbid classes that only have static members
   'unicorn/no-static-only-class': ERROR,
+  // disallow `then` property
+  'unicorn/no-thenable': ERROR,
   // disallow unreadable array destructuring
   'unicorn/no-unreadable-array-destructuring': ERROR,
   // disallow unused object properties
@@ -402,6 +404,8 @@ const base = {
   'unicorn/no-useless-fallback-in-spread': ERROR,
   // disallow useless array length check
   'unicorn/no-useless-length-check': ERROR,
+  // disallow returning / yielding `Promise.{ resolve, reject }` in async functions or promise callbacks
+  'unicorn/no-useless-promise-resolve-reject': ERROR,
   // disallow useless spread
   'unicorn/no-useless-spread': ERROR,
   // enforce lowercase identifier and uppercase value for number literals
@@ -412,10 +416,14 @@ const base = {
   'unicorn/prefer-code-point': ERROR,
   // prefer default parameters over reassignment
   'unicorn/prefer-default-parameters': ERROR,
+  // prefer reading a `JSON` file as a buffer
+  'unicorn/prefer-json-parse-buffer': ERROR,
   // prefer `String#slice` over `String#{ substr, substring }`
   'unicorn/prefer-string-slice': ERROR,
   // prefer `switch` over multiple `else-if`
   'unicorn/prefer-switch': [ERROR, { minimumCases: 3 }],
+  // enforce consistent relative `URL` style
+  'unicorn/relative-url-style': [ERROR, ALWAYS],
   // enforce using the separator argument with `Array#join()`
   'unicorn/require-array-join-separator': ERROR,
   // enforce using the digits argument with `Number#toFixed()`
diff --git a/package.json b/package.json
index f9d9bffa38e5..a218a21d6853 100644
--- a/package.json
+++ b/package.json
@@ -43,7 +43,7 @@
     "eslint-plugin-qunit": "^7.2.0",
     "eslint-plugin-regexp": "^1.5.1",
     "eslint-plugin-sonarjs": "~0.11.0",
-    "eslint-plugin-unicorn": "^39.0.0",
+    "eslint-plugin-unicorn": "^40.0.0",
     "jsonc-eslint-parser": "^2.0.4",
     "karma": "^6.3.9",
     "karma-phantomjs-launcher": "~1.0.4",
diff --git a/packages/core-js/internals/native-url.js b/packages/core-js/internals/native-url.js
index b9ac5878db81..8435fff5ffdd 100644
--- a/packages/core-js/internals/native-url.js
+++ b/packages/core-js/internals/native-url.js
@@ -5,6 +5,7 @@ var IS_PURE = require('../internals/is-pure');
 var ITERATOR = wellKnownSymbol('iterator');
 
 module.exports = !fails(function () {
+  // eslint-disable-next-line unicorn/relative-url-style -- required for testing
   var url = new URL('b?a=1&b=2&c=3', 'http://a');
   var searchParams = url.searchParams;
   var result = '';
diff --git a/packages/core-js/modules/es.promise.finally.js b/packages/core-js/modules/es.promise.finally.js
index eb7153430b85..d105b67d237d 100644
--- a/packages/core-js/modules/es.promise.finally.js
+++ b/packages/core-js/modules/es.promise.finally.js
@@ -11,6 +11,7 @@ var redefine = require('../internals/redefine');
 
 // Safari bug https://bugs.webkit.org/show_bug.cgi?id=200829
 var NON_GENERIC = !!NativePromise && fails(function () {
+  // eslint-disable-next-line unicorn/no-thenable -- required for testing
   NativePromise.prototype['finally'].call({ then: function () { /* empty */ } }, function () { /* empty */ });
 });
 
diff --git a/packages/core-js/modules/es.promise.js b/packages/core-js/modules/es.promise.js
index 9541ac54a544..b6a15faf7c2a 100644
--- a/packages/core-js/modules/es.promise.js
+++ b/packages/core-js/modules/es.promise.js
@@ -265,6 +265,7 @@ if (FORCED) {
   Internal.prototype = redefineAll(PromisePrototype, {
     // `Promise.prototype.then` method
     // https://tc39.es/ecma262/#sec-promise.prototype.then
+    // eslint-disable-next-line unicorn/no-thenable -- safe
     then: function then(onFulfilled, onRejected) {
       var state = getInternalPromiseState(this);
       var reaction = newPromiseCapability(speciesConstructor(this, PromiseConstructor));
diff --git a/packages/core-js/postinstall.js b/packages/core-js/postinstall.js
index 144aa16474c4..e366c39865d8 100644
--- a/packages/core-js/postinstall.js
+++ b/packages/core-js/postinstall.js
@@ -38,7 +38,7 @@ function isBannerRequired() {
   try {
     var DELTA = Date.now() - fs.statSync(file).mtime;
     if (DELTA >= 0 && DELTA < MINUTE * 3) {
-      banners = JSON.parse(fs.readFileSync(file, 'utf8'));
+      banners = JSON.parse(fs.readFileSync(file));
       if (banners.indexOf(BANNER) !== -1) return false;
     }
   } catch (error) {
diff --git a/tests/compat/tests.js b/tests/compat/tests.js
index 060b20126392..57648140993c 100644
--- a/tests/compat/tests.js
+++ b/tests/compat/tests.js
@@ -65,6 +65,7 @@ var SYMBOLS_SUPPORT = function () {
 };
 
 var URL_AND_URL_SEARCH_PARAMS_SUPPORT = function () {
+  // eslint-disable-next-line unicorn/relative-url-style -- required for testing
   var url = new URL('b?a=1&b=2&c=3', 'http://a');
   var searchParams = url.searchParams;
   var result = '';
@@ -805,6 +806,7 @@ GLOBAL.tests = {
     return Promise.any;
   },
   'es.promise.finally': [PROMISES_SUPPORT, function () {
+    // eslint-disable-next-line unicorn/no-thenable -- required for testing
     return Promise.prototype['finally'].call({ then: function () { return this; } }, function () { /* empty */ });
   }],
   'es.reflect.apply': function () {
diff --git a/tests/pure/es.promise.js b/tests/pure/es.promise.js
index 830d4f80155f..d85f95a5d893 100644
--- a/tests/pure/es.promise.js
+++ b/tests/pure/es.promise.js
@@ -1,3 +1,4 @@
+/* eslint-disable unicorn/no-thenable -- required for testing */
 import { DESCRIPTORS, GLOBAL, PROTO, STRICT } from '../helpers/constants';
 import { createIterable } from '../helpers/helpers';
 
diff --git a/tests/pure/web.url.js b/tests/pure/web.url.js
index 197b2abea52b..c7c2ebe45f27 100644
--- a/tests/pure/web.url.js
+++ b/tests/pure/web.url.js
@@ -1,4 +1,4 @@
-/* eslint-disable es/no-object-getownpropertydescriptor -- safe */
+/* eslint-disable es/no-object-getownpropertydescriptor, unicorn/relative-url-style -- required for testing */
 import { DESCRIPTORS, NODE } from '../helpers/constants';
 import urlTestData from '../wpt-url-resources/urltestdata';
 import settersTestData from '../wpt-url-resources/setters';
diff --git a/tests/tests/es.promise.js b/tests/tests/es.promise.js
index 4f143d4be37b..dec783e23959 100644
--- a/tests/tests/es.promise.js
+++ b/tests/tests/es.promise.js
@@ -1,3 +1,4 @@
+/* eslint-disable unicorn/no-thenable -- required for testing */
 import { DESCRIPTORS, GLOBAL, NATIVE, PROTO, STRICT } from '../helpers/constants';
 import { createIterable } from '../helpers/helpers';
 
diff --git a/tests/tests/web.url.js b/tests/tests/web.url.js
index 4112d01d3c5a..05934b0d1080 100644
--- a/tests/tests/web.url.js
+++ b/tests/tests/web.url.js
@@ -1,3 +1,4 @@
+/* eslint-disable unicorn/relative-url-style -- required for testing */
 import { DESCRIPTORS, NODE } from '../helpers/constants';
 import urlTestData from '../wpt-url-resources/urltestdata';
 import settersTestData from '../wpt-url-resources/setters';