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diff --git a/remote/marionette/l10n.sys.mjs b/remote/marionette/l10n.sys.mjs
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+/* 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/. */
+
+/**
+ * An API which allows Marionette to handle localized content.
+ *
+ * The localization (https://mzl.la/2eUMjyF) of UI elements in Gecko
+ * based applications is done via entities and properties. For static
+ * values entities are used, which are located in .dtd files. Whereby for
+ * dynamically updated content the values come from .property files. Both
+ * types of elements can be identifed via a unique id, and the translated
+ * content retrieved.
+ */
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  error: "chrome://remote/content/shared/webdriver/Errors.sys.mjs",
+});
+
+ChromeUtils.defineLazyGetter(lazy, "domParser", () => {
+  const parser = new DOMParser();
+  parser.forceEnableDTD();
+  return parser;
+});
+
+/** @namespace */
+export const l10n = {};
+
+/**
+ * Retrieve the localized string for the specified entity id.
+ *
+ * Example:
+ *     localizeEntity(["chrome://branding/locale/brand.dtd"], "brandShortName")
+ *
+ * @param {Array.<string>} urls
+ *     Array of .dtd URLs.
+ * @param {string} id
+ *     The ID of the entity to retrieve the localized string for.
+ *
+ * @returns {string}
+ *     The localized string for the requested entity.
+ */
+l10n.localizeEntity = function (urls, id) {
+  // Build a string which contains all possible entity locations
+  let locations = [];
+  urls.forEach((url, index) => {
+    locations.push(`<!ENTITY % dtd_${index} SYSTEM "${url}">%dtd_${index};`);
+  });
+
+  // Use the DOM parser to resolve the entity and extract its real value
+  let header = `<?xml version="1.0"?><!DOCTYPE elem [${locations.join("")}]>`;
+  let elem = `<elem id="elementID">&${id};</elem>`;
+  let doc = lazy.domParser.parseFromString(header + elem, "text/xml");
+  let element = doc.querySelector("elem[id='elementID']");
+
+  if (element === null) {
+    throw new lazy.error.NoSuchElementError(
+      `Entity with id='${id}' hasn't been found`
+    );
+  }
+
+  return element.textContent;
+};
+
+/**
+ * Retrieve the localized string for the specified property id.
+ *
+ * Example:
+ *
+ *     localizeProperty(
+ *         ["chrome://global/locale/findbar.properties"], "FastFind");
+ *
+ * @param {Array.<string>} urls
+ *     Array of .properties URLs.
+ * @param {string} id
+ *     The ID of the property to retrieve the localized string for.
+ *
+ * @returns {string}
+ *     The localized string for the requested property.
+ */
+l10n.localizeProperty = function (urls, id) {
+  let property = null;
+
+  for (let url of urls) {
+    let bundle = Services.strings.createBundle(url);
+    try {
+      property = bundle.GetStringFromName(id);
+      break;
+    } catch (e) {}
+  }
+
+  if (property === null) {
+    throw new lazy.error.NoSuchElementError(
+      `Property with ID '${id}' hasn't been found`
+    );
+  }
+
+  return property;
+};