diff --git a/background/style-manager.js b/background/style-manager.js
index d772c59b..1af60bef 100644
--- a/background/style-manager.js
+++ b/background/style-manager.js
@@ -1,6 +1,6 @@
 /* eslint no-eq-null: 0, eqeqeq: [2, "smart"] */
 /* global createCache db calcStyleDigest db tryRegExp styleCodeEmpty styleSectionGlobal
-  getStyleWithNoCode msg prefs sync uuidv4 URLS */
+  getStyleWithNoCode msg prefs sync URLS */
 /* exported styleManager */
 'use strict';
 
@@ -716,4 +716,17 @@ const styleManager = (() => {
       return DUMMY_URL;
     }
   }
+
+  function uuidv4() {
+    const seeds = crypto.getRandomValues(new Uint16Array(8));
+    // 00001111-2222-M333-N444-555566667777
+    seeds[3] = seeds[3] & 0x0FFF | 0x4000; // UUID version 4, M = 4
+    seeds[4] = seeds[4] & 0x3FFF | 0x8000; // UUID variant 1, N = 8..0xB
+    return Array.from(seeds, hex4dashed).join('');
+  }
+
+  /** uuidv4 helper: converts to a 4-digit hex string and adds "-" at required positions */
+  function hex4dashed(num, i) {
+    return (num + 0x10000).toString(16).slice(-4) + (i >= 1 && i <= 4 ? '-' : '');
+  }
 })();
diff --git a/manifest.json b/manifest.json
index 887160ee..faf9d0ca 100644
--- a/manifest.json
+++ b/manifest.json
@@ -40,7 +40,6 @@
       "js/cache.js",
       "vendor/semver-bundle/semver.js",
       "vendor/db-to-cloud/db-to-cloud.min.js",
-      "vendor/uuid/uuid.min.js",
       "vendor/webext-launch-web-auth-flow/webext-launch-web-auth-flow.min.js",
       "background/token-manager.js",
       "background/sync.js",
diff --git a/package-lock.json b/package-lock.json
index 86c23d51..bb64deca 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -7827,11 +7827,6 @@
       "integrity": "sha1-RQ1Nyfpw3nMnYvvS1KKJgUGaDM8=",
       "dev": true
     },
-    "uuid": {
-      "version": "8.1.0",
-      "resolved": "https://registry.npmjs.org/uuid/-/uuid-8.1.0.tgz",
-      "integrity": "sha512-CI18flHDznR0lq54xBycOVmphdCYnQLKn8abKn7PXUiKUGdEd+/l9LWNJmugXel4hXq7S+RMNl34ecyC9TntWg=="
-    },
     "v8-compile-cache": {
       "version": "2.1.1",
       "resolved": "https://registry.npmjs.org/v8-compile-cache/-/v8-compile-cache-2.1.1.tgz",
diff --git a/package.json b/package.json
index f1e83fea..5ede7b19 100644
--- a/package.json
+++ b/package.json
@@ -15,7 +15,6 @@
     "stylelint-bundle": "^8.0.0",
     "stylus-lang-bundle": "^0.54.5",
     "usercss-meta": "^0.9.0",
-    "uuid": "^8.1.0",
     "webext-launch-web-auth-flow": "^0.1.0"
   },
   "devDependencies": {
diff --git a/tools/build-vendor.js b/tools/build-vendor.js
index 639a74ab..41279fb2 100644
--- a/tools/build-vendor.js
+++ b/tools/build-vendor.js
@@ -60,9 +60,6 @@ const files = {
   'db-to-cloud': [
     'dist/db-to-cloud.min.js → db-to-cloud.min.js'
   ],
-  'uuid': [
-    'dist/umd/uuidv4.min.js → uuid.min.js'
-  ],
   'webext-launch-web-auth-flow': [
     'dist/webext-launch-web-auth-flow.min.js → webext-launch-web-auth-flow.min.js'
   ]
diff --git a/vendor/uuid/LICENSE b/vendor/uuid/LICENSE
deleted file mode 100644
index f8969d33..00000000
--- a/vendor/uuid/LICENSE
+++ /dev/null
@@ -1,21 +0,0 @@
-The MIT License (MIT)
-
-Copyright (c) 2010-2020 Robert Kieffer and other contributors
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
diff --git a/vendor/uuid/README.md b/vendor/uuid/README.md
deleted file mode 100644
index 623fe75e..00000000
--- a/vendor/uuid/README.md
+++ /dev/null
@@ -1,5 +0,0 @@
-## uuid v8.1.0
-
-Following files are copied from npm (node_modules):
-
-* uuid.min.js: dist\umd\uuidv4.min.js
diff --git a/vendor/uuid/uuid.min.js b/vendor/uuid/uuid.min.js
deleted file mode 100644
index 61da7182..00000000
--- a/vendor/uuid/uuid.min.js
+++ /dev/null
@@ -1 +0,0 @@
-!function(t,e){"object"==typeof exports&&"undefined"!=typeof module?module.exports=e():"function"==typeof define&&define.amd?define(e):(t=t||self).uuidv4=e()}(this,(function(){"use strict";var t="undefined"!=typeof crypto&&crypto.getRandomValues&&crypto.getRandomValues.bind(crypto)||"undefined"!=typeof msCrypto&&"function"==typeof msCrypto.getRandomValues&&msCrypto.getRandomValues.bind(msCrypto),e=new Uint8Array(16);function n(){if(!t)throw new Error("crypto.getRandomValues() not supported. See https://github.com/uuidjs/uuid#getrandomvalues-not-supported");return t(e)}for(var o=[],r=0;r<256;++r)o.push((r+256).toString(16).substr(1));return function(t,e,r){"string"==typeof t&&(e="binary"===t?new Uint8Array(16):null,t=null);var u=(t=t||{}).random||(t.rng||n)();if(u[6]=15&u[6]|64,u[8]=63&u[8]|128,e){for(var i=r||0,d=0;d<16;++d)e[i+d]=u[d];return e}return function(t,e){var n=e||0,r=o;return(r[t[n+0]]+r[t[n+1]]+r[t[n+2]]+r[t[n+3]]+"-"+r[t[n+4]]+r[t[n+5]]+"-"+r[t[n+6]]+r[t[n+7]]+"-"+r[t[n+8]]+r[t[n+9]]+"-"+r[t[n+10]]+r[t[n+11]]+r[t[n+12]]+r[t[n+13]]+r[t[n+14]]+r[t[n+15]]).toLowerCase()}(u)}}));
\ No newline at end of file