diff --git a/.eslintrc-rollouts.js b/.eslintrc-rollouts.js
index b0e41056e886..68460242d191 100644
--- a/.eslintrc-rollouts.js
+++ b/.eslintrc-rollouts.js
@@ -1992,6 +1992,7 @@ const rollouts = [
     // TODO: Bug TBD - Finish enabling no-shadow with builtinGlobals: true
     // for system modules.
     files: [
+      "browser/components/extensions/Extension*.sys.mjs",
       "docshell/base/URIFixup.sys.mjs",
       "dom/base/ContentAreaDropListener.sys.mjs",
       "dom/manifest/ImageObjectProcessor.sys.mjs",
@@ -2028,6 +2029,54 @@ const rollouts = [
       "no-shadow": ["warn", { allow: ["event"], builtinGlobals: true }],
     },
   },
+  {
+    files: [
+      "browser/components/extensions/**",
+      "docshell/test/**",
+      "devtools/client/framework/**",
+      "dom/fetch/tests/**",
+      "dom/indexedDB/test/**",
+      "dom/media/**",
+      "dom/notification/test/browser/browser_permission_dismiss.js",
+      "dom/security/**",
+      "dom/tests/browser/**",
+      "dom/xslt/tests/browser/file_bug1309630.html",
+      "extensions/spellcheck/tests/chrome/test_add_remove_dictionaries.xhtml",
+      "gfx/layers/layerviewer/layerTreeView.js",
+      "image/test/browser/browser_animated_css_image.js",
+      "js/src/builtin/Promise.js",
+      "js/xpconnect/tests/**",
+      "layout/tools/reftest/reftest-content.js",
+      "mobile/android/geckoview/**",
+      "mobile/shared/components/extensions/**",
+      "netwerk/**",
+      "remote/cdp/**",
+      "remote/shared/**",
+      "remote/webdriver-bidi/**",
+      "security/manager/**",
+      "security/sandbox/**",
+      "taskcluster/docker/periodic-updates/scripts/genHPKPStaticPins.js",
+      "testing/condprofile/condprof/scenarii/bookmark.js",
+      "testing/**",
+      "toolkit/components/**",
+      "toolkit/content/**",
+      "toolkit/crashreporter/**",
+      "toolkit/modules/subprocess/subprocess_shared.js",
+      "toolkit/modules/tests/**",
+      "toolkit/mozapps/**",
+      "toolkit/themes/shared/design-system/tests/try-runner.js",
+      "tools/profiler/tests/**",
+      "tools/tryselect/selectors/chooser/static/filter.js",
+    ],
+    excludedFiles: [
+      "**/*.sys.mjs",
+      "toolkit/components/narrate/**",
+      "toolkit/components/reader/**",
+    ],
+    rules: {
+      "no-shadow": "off",
+    },
+  },
 ];
 
 module.exports = { rollouts };
diff --git a/.eslintrc.js b/.eslintrc.js
index f43504477d6a..0d3fdc7dd64e 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -29,9 +29,9 @@ function removeOverrides(config) {
   return config;
 }
 
-function readFile(path) {
+function readFile(filePath) {
   return fs
-    .readFileSync(path, { encoding: "utf-8" })
+    .readFileSync(filePath, { encoding: "utf-8" })
     .split("\n")
     .filter(p => p && !p.startsWith("#"));
 }
@@ -154,7 +154,7 @@ module.exports = {
     },
     {
       ...removeOverrides(xpcshellTestConfig),
-      files: testPaths.xpcshell.map(path => `${path}**`),
+      files: testPaths.xpcshell.map(filePath => `${filePath}**`),
       excludedFiles: ["**/*.jsm", "**/*.mjs", "**/*.sjs"],
     },
     {
@@ -162,7 +162,7 @@ module.exports = {
       // would require searching the other test files to know if they are used or not.
       // This would be expensive and slow, and it isn't worth it for head files.
       // We could get developers to declare as exported, but that doesn't seem worth it.
-      files: testPaths.xpcshell.map(path => `${path}head*.js`),
+      files: testPaths.xpcshell.map(filePath => `${filePath}head*.js`),
       rules: {
         "no-unused-vars": [
           "error",
@@ -179,7 +179,7 @@ module.exports = {
       // This is not done in the xpcshell-test configuration as we cannot pull
       // in overrides from there. We should at some stage, aim to enable this
       // for all files in xpcshell-tests.
-      files: testPaths.xpcshell.map(path => `${path}test*.js`),
+      files: testPaths.xpcshell.map(filePath => `${filePath}test*.js`),
       rules: {
         // No declaring variables that are never used
         "no-unused-vars": [
@@ -193,12 +193,12 @@ module.exports = {
     },
     {
       ...removeOverrides(browserTestConfig),
-      files: testPaths.browser.map(path => `${path}**`),
+      files: testPaths.browser.map(filePath => `${filePath}**`),
       excludedFiles: ["**/*.jsm", "**/*.mjs", "**/*.sjs"],
     },
     {
       ...removeOverrides(mochitestTestConfig),
-      files: testPaths.mochitest.map(path => `${path}**`),
+      files: testPaths.mochitest.map(filePath => `${filePath}**`),
       excludedFiles: [
         "**/*.jsm",
         "**/*.mjs",
@@ -207,7 +207,7 @@ module.exports = {
     },
     {
       ...removeOverrides(chromeTestConfig),
-      files: testPaths.chrome.map(path => `${path}**`),
+      files: testPaths.chrome.map(filePath => `${filePath}**`),
       excludedFiles: ["**/*.jsm", "**/*.mjs", "**/*.sjs"],
     },
     {
@@ -218,8 +218,8 @@ module.exports = {
         "mozilla/simpletest": true,
       },
       files: [
-        ...testPaths.mochitest.map(path => `${path}/**/*.js`),
-        ...testPaths.chrome.map(path => `${path}/**/*.js`),
+        ...testPaths.mochitest.map(filePath => `${filePath}/**/*.js`),
+        ...testPaths.chrome.map(filePath => `${filePath}/**/*.js`),
       ],
       excludedFiles: ["**/*.jsm", "**/*.mjs", "**/*.sjs"],
     },
@@ -228,7 +228,7 @@ module.exports = {
       // don't work well for HTML-based mochitests, so disable those.
       files: testPaths.xpcshell
         .concat(testPaths.browser)
-        .map(path => [`${path}/**/*.html`, `${path}/**/*.xhtml`])
+        .map(filePath => [`${filePath}/**/*.html`, `${filePath}/**/*.xhtml`])
         .flat(),
       rules: {
         // plain/chrome mochitests don't automatically include Assert, so
@@ -269,7 +269,7 @@ module.exports = {
     },
     {
       // Exempt files with these paths since they have to use http for full coverage
-      files: httpTestingPaths.map(path => `${path}**`),
+      files: httpTestingPaths.map(filePath => `${filePath}**`),
       rules: {
         "@microsoft/sdl/no-insecure-url": "off",
       },
diff --git a/.stylelintrc.js b/.stylelintrc.js
index b0517609b8fc..f42de0b712c6 100644
--- a/.stylelintrc.js
+++ b/.stylelintrc.js
@@ -9,9 +9,9 @@
 const fs = require("fs");
 const path = require("path");
 
-function readFile(path) {
+function readFile(filePath) {
   return fs
-    .readFileSync(path, { encoding: "utf-8" })
+    .readFileSync(filePath, { encoding: "utf-8" })
     .split("\n")
     .filter(p => p && !p.startsWith("#"));
 }
diff --git a/accessible/tests/browser/.eslintrc.js b/accessible/tests/browser/.eslintrc.js
index 96c085946824..90e0c2aefb20 100644
--- a/accessible/tests/browser/.eslintrc.js
+++ b/accessible/tests/browser/.eslintrc.js
@@ -17,7 +17,6 @@ module.exports = {
     "no-multi-str": "error",
     "no-proto": "error",
     "no-return-assign": "error",
-    "no-shadow": "error",
     "no-unused-vars": ["error", { vars: "all", argsIgnorePattern: "^_" }],
     "one-var": ["error", "never"],
     radix: "error",
diff --git a/browser/.eslintrc.js b/browser/.eslintrc.js
index 174e444ee04e..0edc98b551fc 100644
--- a/browser/.eslintrc.js
+++ b/browser/.eslintrc.js
@@ -22,7 +22,5 @@ module.exports = {
 
     // Disallow adding to native types
     "no-extend-native": "error",
-
-    "no-shadow": "error",
   },
 };
diff --git a/browser/components/aboutwelcome/.eslintrc.js b/browser/components/aboutwelcome/.eslintrc.js
index 0048e8275320..401f757329f6 100644
--- a/browser/components/aboutwelcome/.eslintrc.js
+++ b/browser/components/aboutwelcome/.eslintrc.js
@@ -151,7 +151,6 @@ module.exports = {
     "no-prototype-builtins": "error",
     "no-return-assign": ["error", "except-parens"],
     "no-script-url": "error",
-    "no-shadow": "error",
     "no-template-curly-in-string": "error",
     "no-undef-init": "error",
     "no-unmodified-loop-condition": "error",
diff --git a/browser/components/asrouter/.eslintrc.js b/browser/components/asrouter/.eslintrc.js
index 46585eedb3fb..1b50319aef53 100644
--- a/browser/components/asrouter/.eslintrc.js
+++ b/browser/components/asrouter/.eslintrc.js
@@ -117,7 +117,6 @@ module.exports = {
     "no-prototype-builtins": "error",
     "no-return-assign": ["error", "except-parens"],
     "no-script-url": "error",
-    "no-shadow": "error",
     "no-template-curly-in-string": "error",
     "no-undef-init": "error",
     "no-unmodified-loop-condition": "error",
diff --git a/browser/components/extensions/test/browser/.eslintrc.js b/browser/components/extensions/test/browser/.eslintrc.js
index a0509253d679..e57058ecb1c4 100644
--- a/browser/components/extensions/test/browser/.eslintrc.js
+++ b/browser/components/extensions/test/browser/.eslintrc.js
@@ -4,8 +4,4 @@ module.exports = {
   env: {
     webextensions: true,
   },
-
-  rules: {
-    "no-shadow": 0,
-  },
 };
diff --git a/browser/components/migration/.eslintrc.js b/browser/components/migration/.eslintrc.js
index 41a71782f1c2..c537f54b3c0b 100644
--- a/browser/components/migration/.eslintrc.js
+++ b/browser/components/migration/.eslintrc.js
@@ -12,7 +12,6 @@ module.exports = {
     "no-extend-native": "error",
     "no-multi-str": "error",
     "no-return-assign": "error",
-    "no-shadow": "error",
     "no-unused-vars": ["error", { argsIgnorePattern: "^_", vars: "all" }],
     strict: ["error", "global"],
     yoda: "error",
diff --git a/browser/components/newtab/.eslintrc.js b/browser/components/newtab/.eslintrc.js
index 7fdda287dbe4..5bf00ae2eed8 100644
--- a/browser/components/newtab/.eslintrc.js
+++ b/browser/components/newtab/.eslintrc.js
@@ -141,7 +141,6 @@ module.exports = {
     "no-prototype-builtins": "error",
     "no-return-assign": ["error", "except-parens"],
     "no-script-url": "error",
-    "no-shadow": "error",
     "no-template-curly-in-string": "error",
     "no-undef-init": "error",
     "no-unmodified-loop-condition": "error",
diff --git a/devtools/.eslintrc.js b/devtools/.eslintrc.js
index 909dac7d0da4..86505e71ef34 100644
--- a/devtools/.eslintrc.js
+++ b/devtools/.eslintrc.js
@@ -54,12 +54,6 @@ module.exports = {
         "mozilla/var-only-at-top-level": "off",
       },
     },
-    {
-      files: ["client/framework/**"],
-      rules: {
-        "no-shadow": "off",
-      },
-    },
     {
       files: ["client/framework/**"],
       rules: {
@@ -233,12 +227,6 @@ module.exports = {
     // Disallow use of assignment in return statement. It is preferable for a
     // single line of code to have only one easily predictable effect.
     "no-return-assign": "error",
-    // Warn about declaration of variables already declared in the outer scope.
-    // This isn't an error because it sometimes is useful to use the same name
-    // in a small helper function rather than having to come up with another
-    // random name.
-    // Still, making this a warning can help people avoid being confused.
-    "no-shadow": "error",
     // Disallow global and local variables that aren't used. Allow unused
     // function arguments prefixed with `_`.
     "no-unused-vars": ["error", { argsIgnorePattern: "^_", vars: "all" }],
diff --git a/devtools/client/debugger/src/.eslintrc.js b/devtools/client/debugger/src/.eslintrc.js
index 27afb10b351a..ca439cd5130e 100644
--- a/devtools/client/debugger/src/.eslintrc.js
+++ b/devtools/client/debugger/src/.eslintrc.js
@@ -221,12 +221,6 @@ module.exports = {
     "no-self-compare": 2,
     // Disallow use of comma operator.
     "no-sequences": 2,
-    // Warn about declaration of variables already declared in the outer scope.
-    // This isn't an error because it sometimes is useful to use the same name
-    // in a small helper function rather than having to come up with another
-    // random name.
-    // Still, making this a warning can help people avoid being confused.
-    "no-shadow": 2,
     // Disallow sparse arrays, eg. let arr = [,,2].
     // Array destructuring is fine though:
     // for (let [, breakpointPromise] of aPromises)
diff --git a/dom/indexedDB/test/.eslintrc.js b/dom/indexedDB/test/.eslintrc.js
deleted file mode 100644
index 4cb383ff7aa0..000000000000
--- a/dom/indexedDB/test/.eslintrc.js
+++ /dev/null
@@ -1,7 +0,0 @@
-"use strict";
-
-module.exports = {
-  rules: {
-    "no-shadow": "off",
-  },
-};
diff --git a/toolkit/components/extensions/.eslintrc.js b/toolkit/components/extensions/.eslintrc.js
index 2009e44ec97a..d11c70a4c318 100644
--- a/toolkit/components/extensions/.eslintrc.js
+++ b/toolkit/components/extensions/.eslintrc.js
@@ -163,9 +163,6 @@ module.exports = {
     // single line of code to have only one easily predictable effect.
     "no-return-assign": "error",
 
-    // Don't warn about declaration of variables already declared in the outer scope.
-    "no-shadow": "off",
-
     // Allow use of synchronous methods (not a node environment).
     "no-sync": "off",
 
diff --git a/toolkit/components/extensions/test/browser/.eslintrc.js b/toolkit/components/extensions/test/browser/.eslintrc.js
index ef228570e302..e57058ecb1c4 100644
--- a/toolkit/components/extensions/test/browser/.eslintrc.js
+++ b/toolkit/components/extensions/test/browser/.eslintrc.js
@@ -4,8 +4,4 @@ module.exports = {
   env: {
     webextensions: true,
   },
-
-  rules: {
-    "no-shadow": "off",
-  },
 };
diff --git a/toolkit/components/extensions/test/mochitest/.eslintrc.js b/toolkit/components/extensions/test/mochitest/.eslintrc.js
index a776405c9df3..7802d13962f3 100644
--- a/toolkit/components/extensions/test/mochitest/.eslintrc.js
+++ b/toolkit/components/extensions/test/mochitest/.eslintrc.js
@@ -5,8 +5,4 @@ module.exports = {
     browser: true,
     webextensions: true,
   },
-
-  rules: {
-    "no-shadow": 0,
-  },
 };
diff --git a/toolkit/components/narrate/.eslintrc.js b/toolkit/components/narrate/.eslintrc.js
index bbd5aa34dc06..241d12a0dd0c 100644
--- a/toolkit/components/narrate/.eslintrc.js
+++ b/toolkit/components/narrate/.eslintrc.js
@@ -18,7 +18,6 @@ module.exports = {
     "no-inline-comments": "error",
     "no-multi-str": "error",
     "no-return-assign": "error",
-    "no-shadow": "error",
     strict: ["error", "global"],
     yoda: "error",
   },
diff --git a/toolkit/components/reader/.eslintrc.js b/toolkit/components/reader/.eslintrc.js
index bf83f31ab111..fa17d2bb686e 100644
--- a/toolkit/components/reader/.eslintrc.js
+++ b/toolkit/components/reader/.eslintrc.js
@@ -7,7 +7,6 @@
 module.exports = {
   rules: {
     "no-inner-declarations": "error",
-    "no-shadow": "error",
     "no-unused-vars": ["error", { vars: "all", argsIgnorePattern: "^_" }],
   },
 };
diff --git a/tools/lint/eslint/.eslintrc.js b/tools/lint/eslint/.eslintrc.js
index 762ddba02c6f..55b4784386a3 100644
--- a/tools/lint/eslint/.eslintrc.js
+++ b/tools/lint/eslint/.eslintrc.js
@@ -23,7 +23,6 @@ module.exports = {
   rules: {
     camelcase: ["error", { properties: "never" }],
     "handle-callback-err": ["error", "er"],
-    "no-shadow": "error",
     "no-undef-init": "error",
     "one-var": ["error", "never"],
     strict: ["error", "global"],
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/mochitest-test.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/mochitest-test.js
index 1cf55a345388..d37bca424e1a 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/mochitest-test.js
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/mochitest-test.js
@@ -35,6 +35,5 @@ module.exports = {
     // Turn off use-chromeutils-generateqi as these tests don't have ChromeUtils
     // available.
     "mozilla/use-chromeutils-generateqi": "off",
-    "no-shadow": "error",
   },
 };
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js
index e95418c07869..1435b0b45ff1 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js
@@ -285,7 +285,7 @@ module.exports = {
     "no-sequences": "error",
 
     // No declaring variables from an outer scope
-    // "no-shadow": "error",
+    "no-shadow": "error",
 
     // Disallow throwing literals (eg. throw "error" instead of
     // throw new Error("error")).
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/xpcshell-test.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/xpcshell-test.js
index 79c1121809f9..b903da343621 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/xpcshell-test.js
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/xpcshell-test.js
@@ -58,6 +58,5 @@ module.exports = {
 
     "mozilla/no-comparison-or-assignment-inside-ok": "error",
     "mozilla/no-useless-run-test": "error",
-    "no-shadow": "error",
   },
 };