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diff --git a/browser/components/storybook/.storybook/l10n-pseudo.mjs b/browser/components/storybook/.storybook/l10n-pseudo.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/. */
+
+// Stolen from https://github.com/firefox-devtools/profiler/blob/52a7531662a08d96dc8bd03d25adcdb4c9653b92/src/utils/l10n-pseudo.js
+// Which was stolen from https://hg.mozilla.org/mozilla-central/file/a1f74e8c8fb72390d22054d6b00c28b1a32f6c43/intl/l10n/L10nRegistry.jsm#l425
+
+/**
+ * Pseudolocalizations
+ *
+ * PSEUDO_STRATEGIES is a dict of strategies to be used to modify a
+ * context in order to create pseudolocalizations.  These can be used by
+ * developers to test the localizability of their code without having to
+ * actually speak a foreign language.
+ *
+ * Currently, the following pseudolocales are supported:
+ *
+ *   accented - Ȧȧƈƈḗḗƞŧḗḗḓ Ḗḗƞɠŀīīşħ
+ *
+ *     In Accented English all Latin letters are replaced by accented
+ *     Unicode counterparts which don't impair the readability of the content.
+ *     This allows developers to quickly test if any given string is being
+ *     correctly displayed in its 'translated' form.  Additionally, simple
+ *     heuristics are used to make certain words longer to better simulate the
+ *     experience of international users.
+ *
+ *   bidi - ɥsıʅƃuƎ ıpıԐ
+ *
+ *     Bidi English is a fake RTL locale.  All words are surrounded by
+ *     Unicode formatting marks forcing the RTL directionality of characters.
+ *     In addition, to make the reversed text easier to read, individual
+ *     letters are flipped.
+ *
+ *     Note: The name above is hardcoded to be RTL in case code editors have
+ *     trouble with the RLO and PDF Unicode marks.  In reality, it should be
+ *     surrounded by those marks as well.
+ *
+ * See https://bugzil.la/1450781 for more information.
+ *
+ * In this implementation we use code points instead of inline unicode characters
+ * because the encoding of JSM files mangles them otherwise.
+ */
+
+const ACCENTED_MAP = {
+  // ȦƁƇḒḖƑƓĦĪĴĶĿḾȠǾƤɊŘŞŦŬṼẆẊẎẐ
+  // prettier-ignore
+  "caps": [550, 385, 391, 7698, 7702, 401, 403, 294, 298, 308, 310, 319, 7742, 544, 510, 420, 586, 344, 350, 358, 364, 7804, 7814, 7818, 7822, 7824],
+  // ȧƀƈḓḗƒɠħīĵķŀḿƞǿƥɋřşŧŭṽẇẋẏẑ
+  // prettier-ignore
+  "small": [551, 384, 392, 7699, 7703, 402, 608, 295, 299, 309, 311, 320, 7743, 414, 511, 421, 587, 345, 351, 359, 365, 7805, 7815, 7819, 7823, 7825],
+};
+
+const FLIPPED_MAP = {
+  // ∀ԐↃᗡƎℲ⅁HIſӼ⅂WNOԀÒᴚS⊥∩ɅMX⅄Z
+  // prettier-ignore
+  "caps": [8704, 1296, 8579, 5601, 398, 8498, 8513, 72, 73, 383, 1276, 8514, 87, 78, 79, 1280, 210, 7450, 83, 8869, 8745, 581, 77, 88, 8516, 90],
+  // ɐqɔpǝɟƃɥıɾʞʅɯuodbɹsʇnʌʍxʎz
+  // prettier-ignore
+  "small": [592, 113, 596, 112, 477, 607, 387, 613, 305, 638, 670, 645, 623, 117, 111, 100, 98, 633, 115, 647, 110, 652, 653, 120, 654, 122],
+};
+
+function transformString(
+  map = FLIPPED_MAP,
+  elongate = false,
+  prefix = "",
+  postfix = "",
+  msg
+) {
+  // Exclude access-keys and other single-char messages
+  if (msg.length === 1) {
+    return msg;
+  }
+  // XML entities (&#x202a;) and XML tags.
+  const reExcluded = /(&[#\w]+;|<\s*.+?\s*>)/;
+
+  const parts = msg.split(reExcluded);
+  const modified = parts.map(part => {
+    if (reExcluded.test(part)) {
+      return part;
+    }
+    return (
+      prefix +
+      part.replace(/[a-z]/gi, ch => {
+        const cc = ch.charCodeAt(0);
+        if (cc >= 97 && cc <= 122) {
+          const newChar = String.fromCodePoint(map.small[cc - 97]);
+          // duplicate "a", "e", "o" and "u" to emulate ~30% longer text
+          if (
+            elongate &&
+            (cc === 97 || cc === 101 || cc === 111 || cc === 117)
+          ) {
+            return newChar + newChar;
+          }
+          return newChar;
+        }
+        if (cc >= 65 && cc <= 90) {
+          return String.fromCodePoint(map.caps[cc - 65]);
+        }
+        return ch;
+      }) +
+      postfix
+    );
+  });
+  return modified.join("");
+}
+
+export const PSEUDO_STRATEGY_TRANSFORMS = {
+  accented: transformString.bind(null, ACCENTED_MAP, true, "", ""),
+  bidi: transformString.bind(null, FLIPPED_MAP, false, "\u202e", "\u202c"),
+};