diff --git a/package-lock.json b/package-lock.json
index e2bec3ec..d8843901 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9,6 +9,7 @@
       "version": "0.1.0",
       "dependencies": {
         "@formatjs/intl-localematcher": "~0.5.4",
+        "@formatjs/intl-segmenter": "~11.5.5",
         "@formkit/auto-animate": "~0.8.1",
         "@github/text-expander-element": "~2.6.1",
         "@iconify-icons/mingcute": "~1.2.9",
@@ -33,8 +34,7 @@
         "react-intersection-observer": "~9.8.1",
         "react-quick-pinch-zoom": "~5.1.0",
         "react-router-dom": "6.6.2",
-        "runes2": "~1.1.4",
-        "string-length": "5.0.1",
+        "string-length": "6.0.0",
         "swiped-events": "~1.1.9",
         "toastify-js": "~1.12.0",
         "uid": "~2.0.2",
@@ -2924,6 +2924,15 @@
         "node": ">=12"
       }
     },
+    "node_modules/@formatjs/ecma402-abstract": {
+      "version": "1.18.2",
+      "resolved": "https://registry.npmjs.org/@formatjs/ecma402-abstract/-/ecma402-abstract-1.18.2.tgz",
+      "integrity": "sha512-+QoPW4csYALsQIl8GbN14igZzDbuwzcpWrku9nyMXlaqAlwRBgl5V+p0vWMGFqHOw37czNXaP/lEk4wbLgcmtA==",
+      "dependencies": {
+        "@formatjs/intl-localematcher": "0.5.4",
+        "tslib": "^2.4.0"
+      }
+    },
     "node_modules/@formatjs/intl-localematcher": {
       "version": "0.5.4",
       "resolved": "https://registry.npmjs.org/@formatjs/intl-localematcher/-/intl-localematcher-0.5.4.tgz",
@@ -2932,6 +2941,16 @@
         "tslib": "^2.4.0"
       }
     },
+    "node_modules/@formatjs/intl-segmenter": {
+      "version": "11.5.5",
+      "resolved": "https://registry.npmjs.org/@formatjs/intl-segmenter/-/intl-segmenter-11.5.5.tgz",
+      "integrity": "sha512-mMbJKFGzwYJBcwfL9EfqFje75Ce5WPar5rSi7wWvFtBPFY2Zi1cWIss7FSm2MNNM9l1BycBAsBQuXFt+Hd+0tQ==",
+      "dependencies": {
+        "@formatjs/ecma402-abstract": "1.18.2",
+        "@formatjs/intl-localematcher": "0.5.4",
+        "tslib": "^2.4.0"
+      }
+    },
     "node_modules/@formkit/auto-animate": {
       "version": "0.8.1",
       "resolved": "https://registry.npmjs.org/@formkit/auto-animate/-/auto-animate-0.8.1.tgz",
@@ -3967,15 +3986,6 @@
         "tslib": "^2.0.3"
       }
     },
-    "node_modules/char-regex": {
-      "version": "2.0.1",
-      "resolved": "https://registry.npmjs.org/char-regex/-/char-regex-2.0.1.tgz",
-      "integrity": "sha512-oSvEeo6ZUD7NepqAat3RqoucZ5SeqLJgOvVIwkafu6IP3V0pO38s/ypdVUmDDK6qIIHNlYHJAKX9E7R7HoKElw==",
-      "license": "MIT",
-      "engines": {
-        "node": ">=12.20"
-      }
-    },
     "node_modules/color-convert": {
       "version": "1.9.3",
       "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-1.9.3.tgz",
@@ -7116,11 +7126,6 @@
         "queue-microtask": "^1.2.2"
       }
     },
-    "node_modules/runes2": {
-      "version": "1.1.4",
-      "resolved": "https://registry.npmjs.org/runes2/-/runes2-1.1.4.tgz",
-      "integrity": "sha512-LNPnEDPOOU4ehF71m5JoQyzT2yxwD6ZreFJ7MxZUAoMKNMY1XrAo60H1CUoX5ncSm0rIuKlqn9JZNRrRkNou2g=="
-    },
     "node_modules/safe-buffer": {
       "version": "5.2.1",
       "resolved": "https://registry.npmjs.org/safe-buffer/-/safe-buffer-5.2.1.tgz",
@@ -7262,16 +7267,14 @@
       "license": "MIT"
     },
     "node_modules/string-length": {
-      "version": "5.0.1",
-      "resolved": "https://registry.npmjs.org/string-length/-/string-length-5.0.1.tgz",
-      "integrity": "sha512-9Ep08KAMUn0OadnVaBuRdE2l615CQ508kr0XMadjClfYpdCyvrbFp6Taebo8yyxokQ4viUd/xPPUA4FGgUa0ow==",
-      "license": "MIT",
+      "version": "6.0.0",
+      "resolved": "https://registry.npmjs.org/string-length/-/string-length-6.0.0.tgz",
+      "integrity": "sha512-1U361pxZHEQ+FeSjzqRpV+cu2vTzYeWeafXFLykiFlv4Vc0n3njgU8HrMbyik5uwm77naWMuVG8fhEF+Ovb1Kg==",
       "dependencies": {
-        "char-regex": "^2.0.0",
-        "strip-ansi": "^7.0.1"
+        "strip-ansi": "^7.1.0"
       },
       "engines": {
-        "node": ">=12.20"
+        "node": ">=16"
       },
       "funding": {
         "url": "https://github.com/sponsors/sindresorhus"
diff --git a/package.json b/package.json
index 07d037c8..f4117a77 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,7 @@
   },
   "dependencies": {
     "@formatjs/intl-localematcher": "~0.5.4",
+    "@formatjs/intl-segmenter": "~11.5.5",
     "@formkit/auto-animate": "~0.8.1",
     "@github/text-expander-element": "~2.6.1",
     "@iconify-icons/mingcute": "~1.2.9",
@@ -35,8 +36,7 @@
     "react-intersection-observer": "~9.8.1",
     "react-quick-pinch-zoom": "~5.1.0",
     "react-router-dom": "6.6.2",
-    "runes2": "~1.1.4",
-    "string-length": "5.0.1",
+    "string-length": "6.0.0",
     "swiped-events": "~1.1.9",
     "toastify-js": "~1.12.0",
     "uid": "~2.0.2",
diff --git a/src/components/compose.jsx b/src/components/compose.jsx
index c075790f..001b0f9c 100644
--- a/src/components/compose.jsx
+++ b/src/components/compose.jsx
@@ -6,7 +6,6 @@ import { deepEqual } from 'fast-equals';
 import { forwardRef } from 'preact/compat';
 import { useEffect, useMemo, useRef, useState } from 'preact/hooks';
 import { useHotkeys } from 'react-hotkeys-hook';
-import { substring } from 'runes2';
 import stringLength from 'string-length';
 import { uid } from 'uid/single';
 import { useDebouncedCallback, useThrottledCallback } from 'use-debounce';
@@ -131,6 +130,7 @@ const SCAN_RE = new RegExp(
   'g',
 );
 
+const segmenter = new Intl.Segmenter();
 function highlightText(text, { maxCharacters = Infinity }) {
   // Accept text string, return formatted HTML string
   // Escape all HTML special characters
@@ -143,19 +143,25 @@ function highlightText(text, { maxCharacters = Infinity }) {
 
   // Exceeded characters limit
   const { composerCharacterCount } = states;
-  let leftoverHTML = '';
   if (composerCharacterCount > maxCharacters) {
-    // NOTE: runes2 substring considers surrogate pairs
-    // const leftoverCount = composerCharacterCount - maxCharacters;
     // Highlight exceeded characters
-    leftoverHTML =
-      '<mark class="compose-highlight-exceeded">' +
-      // html.slice(-leftoverCount) +
-      substring(html, maxCharacters) +
-      '</mark>';
-    // html = html.slice(0, -leftoverCount);
-    html = substring(html, 0, maxCharacters);
-    return html + leftoverHTML;
+    let withinLimitHTML = '',
+      exceedLimitHTML = '';
+    const htmlSegments = segmenter.segment(html);
+    for (const { segment, index } of htmlSegments) {
+      if (index < maxCharacters) {
+        withinLimitHTML += segment;
+      } else {
+        exceedLimitHTML += segment;
+      }
+    }
+    if (exceedLimitHTML) {
+      exceedLimitHTML =
+        '<mark class="compose-highlight-exceeded">' +
+        exceedLimitHTML +
+        '</mark>';
+    }
+    return withinLimitHTML + exceedLimitHTML;
   }
 
   return html
diff --git a/src/main.jsx b/src/main.jsx
index 9c21e63f..19a84c69 100644
--- a/src/main.jsx
+++ b/src/main.jsx
@@ -2,6 +2,9 @@ import './index.css';
 
 import './cloak-mode.css';
 
+// Polyfill needed for Firefox < 122
+// https://bugzilla.mozilla.org/show_bug.cgi?id=1423593
+import '@formatjs/intl-segmenter/polyfill';
 import { render } from 'preact';
 import { HashRouter } from 'react-router-dom';