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diff --git a/toolkit/components/extensions/.eslintrc.js b/toolkit/components/extensions/.eslintrc.js
new file mode 100644
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+++ b/toolkit/components/extensions/.eslintrc.js
@@ -0,0 +1,228 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+module.exports = {
+  globals: {
+    // These are defined in the WebExtension script scopes by ExtensionCommon.jsm
+    Cc: true,
+    Ci: true,
+    Cr: true,
+    Cu: true,
+    AppConstants: true,
+    ExtensionAPI: true,
+    ExtensionAPIPersistent: true,
+    ExtensionCommon: true,
+    ExtensionUtils: true,
+    extensions: true,
+    global: true,
+    require: false,
+    Services: true,
+    XPCOMUtils: true,
+  },
+
+  rules: {
+    // Rules from the mozilla plugin
+    "mozilla/balanced-listeners": "error",
+    "mozilla/no-aArgs": "error",
+    "mozilla/var-only-at-top-level": "error",
+    // Disable reject-importGlobalProperties because we don't want to include
+    // these in the sandbox directly as that would potentially mean the
+    // imported properties would be instatiated up-front rather than lazily.
+    "mozilla/reject-importGlobalProperties": "off",
+
+    // Functions are not required to consistently return something or nothing
+    "consistent-return": "off",
+
+    // Disallow empty statements. This will report an error for:
+    // try { something(); } catch (e) {}
+    // but will not report it for:
+    // try { something(); } catch (e) { /* Silencing the error because ...*/ }
+    // which is a valid use case.
+    "no-empty": "error",
+
+    // No expressions where a statement is expected
+    "no-unused-expressions": "error",
+
+    // No declaring variables that are never used
+    "no-unused-vars": [
+      "error",
+      {
+        args: "none",
+        vars: "all",
+        varsIgnorePattern: "^console$",
+      },
+    ],
+
+    // No using variables before defined
+    "no-use-before-define": "error",
+
+    // Disallow using variables outside the blocks they are defined (especially
+    // since only let and const are used, see "no-var").
+    "block-scoped-var": "error",
+
+    // Warn about cyclomatic complexity in functions.
+    complexity: "error",
+
+    // Don't warn for inconsistent naming when capturing this (not so important
+    // with auto-binding fat arrow functions).
+    // "consistent-this": ["error", "self"],
+
+    // Don't require a default case in switch statements. Avoid being forced to
+    // add a bogus default when you know all possible cases are handled.
+    "default-case": "off",
+
+    // Allow using == instead of ===, in the interest of landing something since
+    // the devtools codebase is split on convention here.
+    eqeqeq: "off",
+
+    // Don't require function expressions to have a name.
+    // This makes the code more verbose and hard to read. Our engine already
+    // does a fantastic job assigning a name to the function, which includes
+    // the enclosing function name, and worst case you have a line number that
+    // you can just look up.
+    "func-names": "off",
+
+    // Allow use of function declarations and expressions.
+    "func-style": "off",
+
+    // Maximum depth callbacks can be nested.
+    "max-nested-callbacks": ["error", 4],
+
+    // Don't limit the number of parameters that can be used in a function.
+    "max-params": "off",
+
+    // Don't limit the maximum number of statement allowed in a function. We
+    // already have the complexity rule that's a better measurement.
+    "max-statements": "off",
+
+    // Don't require a capital letter for constructors, only check if all new
+    // operators are followed by a capital letter. Don't warn when capitalized
+    // functions are used without the new operator.
+    "new-cap": ["off", { capIsNew: false }],
+
+    // Allow use of bitwise operators.
+    "no-bitwise": "off",
+
+    // Disallow using the console API.
+    "no-console": "error",
+
+    // Allow using constant expressions in conditions like while (true)
+    "no-constant-condition": "off",
+
+    // Allow use of the continue statement.
+    "no-continue": "off",
+
+    // Allow division operators explicitly at beginning of regular expression.
+    "no-div-regex": "off",
+
+    // Disallow adding to native types
+    "no-extend-native": "error",
+
+    // Disallow fallthrough of case statements, except if there is a comment.
+    "no-fallthrough": "error",
+
+    // Allow comments inline after code.
+    "no-inline-comments": "off",
+
+    // Disallow use of labels for anything other then loops and switches.
+    "no-labels": ["error", { allowLoop: true }],
+
+    // Disallow use of multiline strings (use template strings instead).
+    "no-multi-str": "error",
+
+    // Allow reassignment of function parameters.
+    "no-param-reassign": "off",
+
+    // Allow string concatenation with __dirname and __filename (not a node env).
+    "no-path-concat": "off",
+
+    // Allow use of unary operators, ++ and --.
+    "no-plusplus": "off",
+
+    // Allow using process.env (not a node environment).
+    "no-process-env": "off",
+
+    // Allow using process.exit (not a node environment).
+    "no-process-exit": "off",
+
+    // Disallow usage of __proto__ property.
+    "no-proto": "error",
+
+    // Don't restrict usage of specified node modules (not a node environment).
+    "no-restricted-modules": "off",
+
+    // 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",
+
+    // 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",
+
+    // Allow the use of ternary operators.
+    "no-ternary": "off",
+
+    // Allow dangling underscores in identifiers (for privates).
+    "no-underscore-dangle": "off",
+
+    // Allow use of undefined variable.
+    "no-undefined": "off",
+
+    // We use var-only-at-top-level instead of no-var as we allow top level
+    // vars.
+    "no-var": "off",
+
+    // Allow using TODO/FIXME comments.
+    "no-warning-comments": "off",
+
+    // Don't require method and property shorthand syntax for object literals.
+    // We use this in the code a lot, but not consistently, and this seems more
+    // like something to check at code review time.
+    "object-shorthand": "off",
+
+    // Allow more than one variable declaration per function.
+    "one-var": "off",
+
+    // Require use of the second argument for parseInt().
+    radix: "error",
+
+    // Don't require to sort variables within the same declaration block.
+    // Anyway, one-var is disabled.
+    "sort-vars": "off",
+
+    // Require "use strict" to be defined globally in the script.
+    strict: ["error", "global"],
+
+    // Allow vars to be declared anywhere in the scope.
+    "vars-on-top": "off",
+
+    // Disallow Yoda conditions (where literal value comes first).
+    yoda: "error",
+
+    // Disallow function or variable declarations in nested blocks
+    "no-inner-declarations": "error",
+
+    // Disallow labels that share a name with a variable
+    "no-label-var": "error",
+  },
+
+  overrides: [
+    {
+      files: "test/xpcshell/head*.js",
+      rules: {
+        "no-unused-vars": [
+          "error",
+          {
+            args: "none",
+            vars: "local",
+          },
+        ],
+      },
+    },
+  ],
+};