diff --git a/background/context-menus.js b/background/context-menus.js
index 53101dea..148616af 100644
--- a/background/context-menus.js
+++ b/background/context-menus.js
@@ -1,7 +1,7 @@
 /* global browserCommands */// background.js
 /* global msg */
 /* global prefs */
-/* global CHROME FIREFOX URLS ignoreChromeError */// toolbox.js
+/* global CHROME URLS ignoreChromeError */// toolbox.js
 'use strict';
 
 (() => {
@@ -28,7 +28,7 @@
       click: browserCommands.reload,
     },
     'editor.contextDelete': {
-      presentIf: () => !FIREFOX && prefs.get('editor.contextDelete'),
+      presentIf: () => CHROME && prefs.get('editor.contextDelete'),
       title: 'editDeleteText',
       type: 'normal',
       contexts: ['editable'],
@@ -40,14 +40,7 @@
     },
   };
 
-  // "Delete" item in context menu for browsers that don't have it
-  if (CHROME &&
-      // looking at the end of UA string
-      /(Vivaldi|Safari)\/[\d.]+$/.test(navigator.userAgent) &&
-      // skip forks with Flash as those are likely to have the menu e.g. CentBrowser
-      !Array.from(navigator.plugins).some(p => p.name === 'Shockwave Flash')) {
-    prefs.__defaults['editor.contextDelete'] = true;
-  }
+  prefs.__defaults['editor.contextDelete'] = Boolean(CHROME);
 
   const keys = Object.keys(contextMenus);
   prefs.subscribe(keys.filter(id => typeof prefs.defaults[id] === 'boolean'),
diff --git a/js/dom.js b/js/dom.js
index ff2390c9..dd9f8d62 100644
--- a/js/dom.js
+++ b/js/dom.js
@@ -1,4 +1,4 @@
-/* global FIREFOX debounce */// toolbox.js
+/* global FIREFOX WINDOWS debounce */// toolbox.js
 /* global prefs */
 'use strict';
 
@@ -418,9 +418,7 @@ async function waitForSheet({
   window.on('mousedown', suppressFocusRingOnClick, {passive: true});
   window.on('keydown', keepFocusRingOnTabbing, {passive: true});
 
-  if (!/^Win\d+/.test(navigator.platform)) {
-    document.documentElement.classList.add('non-windows');
-  }
+  document.documentElement.classList.toggle('non-windows', !WINDOWS);
   // set language for a) CSS :lang pseudo and b) hyphenation
   document.documentElement.setAttribute('lang', chrome.i18n.getUILanguage());
   document.on('keypress', clickDummyLinkOnEnter);
diff --git a/js/prefs.js b/js/prefs.js
index 3d7b93fa..67b06852 100644
--- a/js/prefs.js
+++ b/js/prefs.js
@@ -1,5 +1,5 @@
 /* global API msg */// msg.js
-/* global debounce deepMerge */// toolbox.js - not used in content scripts
+/* global MOBILE WINDOWS debounce deepMerge */// toolbox.js - not used in content scripts
 'use strict';
 
 (() => {
@@ -51,7 +51,7 @@
     'manage.backup.expanded': true,
     'manage.filters.expanded': true,
     // the new compact layout doesn't look good on Android yet
-    'manage.newUI': !navigator.appVersion.includes('Android'),
+    'manage.newUI': chrome.tabs ? !MOBILE : false,
     'manage.newUI.favicons': false, // show favicons for the sites in applies-to
     'manage.newUI.faviconsGray': true, // gray out favicons
     'manage.newUI.targets': 3,      // max number of applies-to targets visible: 0 = none
@@ -65,7 +65,7 @@
     'editor.smartIndent': true,     // 'smart' indent
     'editor.indentWithTabs': false, // smart indent with tabs
     'editor.tabSize': 4,            // tab width, in spaces
-    'editor.keyMap': navigator.appVersion.indexOf('Windows') > 0 ? 'sublime' : 'default',
+    'editor.keyMap': chrome.tabs && WINDOWS ? 'sublime' : 'default',
     'editor.theme': 'default',      // CSS theme
     // CSS beautifier
     'editor.beautify': {
diff --git a/js/toolbox.js b/js/toolbox.js
index 55f5422b..5f23587a 100644
--- a/js/toolbox.js
+++ b/js/toolbox.js
@@ -2,7 +2,9 @@
 
 /* exported
   CHROME_POPUP_BORDER_BUG
+  MOBILE
   RX_META
+  WINDOWS
   capitalize
   closeCurrentTab
   deepEqual
@@ -22,10 +24,37 @@
   waitForTabUrl
 */
 
-const CHROME = Boolean(chrome.app) && Number(navigator.userAgent.match(/Chrom\w+\/(\d+)|$/)[1]);
-const OPERA = Boolean(chrome.app) && parseFloat(navigator.userAgent.match(/\bOPR\/(\d+\.\d+)|$/)[1]);
-const VIVALDI = Boolean(chrome.app) && navigator.userAgent.includes('Vivaldi');
-let FIREFOX = !chrome.app && parseFloat(navigator.userAgent.match(/\bFirefox\/(\d+\.\d+)|$/)[1]);
+let {
+  CHROME = false,
+  OPERA = false,
+  VIVALDI = false,
+  FIREFOX = false,
+  Windows: WINDOWS = false,
+  mobile: MOBILE = false,
+  // New Vivaldi doesn't expose itself via `brands` or UA, only via `extData` on a Tab object.
+} = (() => {
+  const MAP = {
+    OPR: 'OPERA',
+    Chromium: 'CHROME',
+    'Google Chrome': 'CHROME',
+  };
+  const uaData = navigator.userAgentData || {
+    // Accessing `userAgent` shows a warning in devtools.
+    brands: navigator.userAgent.match(/\b(\w+)\/(\d+\.\d+)/g)
+      .map(s => s.split('/'))
+      .map(([brand, version]) => ({brand, version})),
+    mobile: navigator.userAgent.includes('Android'),
+  };
+  const res = {
+    mobile: uaData.mobile,
+    // Vivaldi bug: no `platform` in uaData
+    [uaData.platform || navigator.userAgent.match(/\((\S+)|$/)[1]]: true,
+  };
+  for (const {brand, version} of uaData.brands) {
+    res[MAP[brand] || brand.toUpperCase()] = Number(version);
+  }
+  return res;
+})();
 
 // see PR #781
 const CHROME_POPUP_BORDER_BUG = CHROME >= 62 && CHROME <= 74;