diff --git a/_locales/en/messages.json b/_locales/en/messages.json
index e54155ec..c9fb1aa6 100644
--- a/_locales/en/messages.json
+++ b/_locales/en/messages.json
@@ -1530,6 +1530,14 @@
     "message": "The value cannot be saved. Try reducing the amount of text.",
     "description": "Displayed when trying to save an excessively big value via storage.sync API"
   },
+  "syncError": {
+    "message": "Sync failed",
+    "description": "Tooltip for the toolbar icon"
+  },
+  "syncErrorRelogin": {
+    "message": "Sync failed.\nTry to re-login in Stylus options:\nclick 'disconnect' first, then 'connect'.",
+    "description": "Tooltip for the toolbar icon"
+  },
   "toggleStyle": {
     "message": "Toggle style",
     "description": "Label for the checkbox to enable/disable a style"
diff --git a/background/icon-manager.js b/background/icon-manager.js
index 5d51e8e7..5e13a15c 100644
--- a/background/icon-manager.js
+++ b/background/icon-manager.js
@@ -5,10 +5,12 @@
 /* global CHROME FIREFOX VIVALDI debounce ignoreChromeError */// toolbox.js
 'use strict';
 
-(() => {
+/* exported iconMan */
+const iconMan = (() => {
   const ICON_SIZES = FIREFOX || CHROME >= 55 && !VIVALDI ? [16, 32] : [19, 38];
   const staleBadges = new Set();
   const imageDataCache = new Map();
+  const badgeOvr = {color: '', text: ''};
   // https://github.com/openstyles/stylus/issues/335
   let hasCanvas = loadImage(`/images/icon/${ICON_SIZES[0]}.png`)
     .then(({data}) => (hasCanvas = data.some(b => b !== 255)));
@@ -54,6 +56,27 @@
     ], () => debounce(refreshAllIcons), {runNow: true});
   });
 
+  return {
+    /** Calling with no params clears the override */
+    overrideBadge({text = '', color = '', title = ''} = {}) {
+      if (badgeOvr.text === text) {
+        return;
+      }
+      badgeOvr.text = text;
+      badgeOvr.color = color;
+      refreshIconBadgeColor();
+      setBadgeText({text});
+      for (const tabId of tabMan.list()) {
+        if (badgeOvr) {
+          setBadgeText({tabId, text});
+        } else {
+          refreshIconBadgeText(tabId);
+        }
+      }
+      chrome.browserAction.setTitle({title});
+    },
+  };
+
   function onPortDisconnected({sender}) {
     if (tabMan.get(sender.tab.id, 'styleIds')) {
       API.updateIconBadge.call({sender}, [], {lazyBadge: true});
@@ -61,6 +84,7 @@
   }
 
   function refreshIconBadgeText(tabId) {
+    if (badgeOvr.text) return;
     const text = prefs.get('show-badge') ? `${getStyleCount(tabId)}` : '';
     setBadgeText({tabId, text});
   }
@@ -133,9 +157,9 @@
   }
 
   function refreshIconBadgeColor() {
-    const color = prefs.get(prefs.get('disableAll') ? 'badgeDisabled' : 'badgeNormal');
     setBadgeBackgroundColor({
-      color,
+      color: badgeOvr.color ||
+        prefs.get(prefs.get('disableAll') ? 'badgeDisabled' : 'badgeNormal'),
     });
   }
 
diff --git a/background/sync-manager.js b/background/sync-manager.js
index 0d5938f5..db816a1e 100644
--- a/background/sync-manager.js
+++ b/background/sync-manager.js
@@ -1,6 +1,7 @@
 /* global API msg */// msg.js
 /* global chromeLocal */// storage-util.js
 /* global compareRevision */// common.js
+/* global iconMan */
 /* global prefs */
 /* global tokenMan */
 'use strict';
@@ -26,6 +27,7 @@ const syncMan = (() => {
     errorMessage: null,
     login: false,
   };
+  let lastError = null;
   let ctrl;
   let currentDrive;
   /** @type {Promise|boolean} will be `true` to avoid wasting a microtask tick on each `await` */
@@ -99,8 +101,10 @@ const syncMan = (() => {
         }
         await syncMan.syncNow();
         status.errorMessage = null;
+        lastError = null;
       } catch (err) {
         status.errorMessage = err.message;
+        lastError = err;
         // FIXME: should we move this logic to options.js?
         if (!fromPref) {
           console.error(err);
@@ -138,8 +142,10 @@ const syncMan = (() => {
       try {
         await (ctrl.isInit() ? ctrl.syncNow() : ctrl.start()).catch(handle401Error);
         status.errorMessage = null;
+        lastError = null;
       } catch (err) {
         status.errorMessage = err.message;
+        lastError = err;
       }
       emitStatusChange();
     },
@@ -187,14 +193,14 @@ const syncMan = (() => {
   }
 
   async function handle401Error(err) {
-    let emit;
+    let authError = false;
     if (err.code === 401) {
       await tokenMan.revokeToken(currentDrive.name).catch(console.error);
-      emit = true;
+      authError = true;
     } else if (/User interaction required|Requires user interaction/i.test(err.message)) {
-      emit = true;
+      authError = true;
     }
-    if (emit) {
+    if (authError) {
       status.login = false;
       emitStatusChange();
     }
@@ -203,6 +209,32 @@ const syncMan = (() => {
 
   function emitStatusChange() {
     msg.broadcastExtension({method: 'syncStatusUpdate', status});
+
+    if (status.state !== STATES.connected || !lastError || isNetworkError(lastError)) {
+      iconMan.overrideBadge({});
+    } else if (isGrantError(lastError)) {
+      iconMan.overrideBadge({
+        text: 'x',
+        color: '#F00',
+        title: chrome.i18n.getMessage('syncErrorRelogin'),
+      });
+    } else {
+      iconMan.overrideBadge({
+        text: 'x',
+        color: '#F00',
+        title: chrome.i18n.getMessage('syncError'),
+      });
+    }
+  }
+
+  function isNetworkError(err) {
+    return err.name === 'TypeError' && /networkerror|failed to fetch/i.test(err.message);
+  }
+
+  function isGrantError(err) {
+    if (err.code === 401) return true;
+    if (err.code === 400 && /invalid_grant/.test(err.message)) return true;
+    return false;
   }
 
   function getDrive(name) {
diff --git a/background/tab-manager.js b/background/tab-manager.js
index ca5b183d..0a1fea07 100644
--- a/background/tab-manager.js
+++ b/background/tab-manager.js
@@ -53,6 +53,7 @@ const tabMan = (() => {
       }
     },
 
+    /** @returns {IterableIterator<number>} */
     list() {
       return cache.keys();
     },
diff --git a/package-lock.json b/package-lock.json
index 6abf6ec6..9fce00ac 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -645,7 +645,6 @@
         "espree": "7.3.0",
         "esprima": "4.0.1",
         "fluent-syntax": "0.13.0",
-        "fsevents": "2.2.1",
         "glob": "7.1.6",
         "is-mergeable-object": "1.1.1",
         "jed": "1.1.1",
@@ -1855,12 +1854,6 @@
       "engines": [
         "node >=0.10.0"
       ],
-      "dependencies": {
-        "dtrace-provider": "~0.8",
-        "moment": "^2.19.3",
-        "mv": "~2",
-        "safe-json-stringify": "~1"
-      },
       "bin": {
         "bunyan": "bin/bunyan"
       },
@@ -2144,7 +2137,6 @@
       "dependencies": {
         "anymatch": "~3.1.1",
         "braces": "~3.0.2",
-        "fsevents": "~2.1.2",
         "glob-parent": "~5.1.0",
         "is-binary-path": "~2.1.0",
         "is-glob": "~4.0.1",
@@ -4559,9 +4551,6 @@
       "resolved": "https://registry.npmjs.org/jsonfile/-/jsonfile-4.0.0.tgz",
       "integrity": "sha1-h3Gq4HmbZAdrdmQPygWPnBDjPss=",
       "dev": true,
-      "dependencies": {
-        "graceful-fs": "^4.1.6"
-      },
       "optionalDependencies": {
         "graceful-fs": "^4.1.6"
       }
@@ -6995,7 +6984,6 @@
       "integrity": "sha512-ssHt0dkljEDaKmTgQ04DQgx2ag6G2gMPxA5hpcsoeTbfDgRf2fC2gNSRc6kISjD7ckCpHwwQvXxuTBK8402fXg==",
       "dev": true,
       "dependencies": {
-        "encoding": "^0.1.12",
         "minipass": "^3.1.0",
         "minipass-pipeline": "^1.2.2",
         "minipass-sized": "^1.0.3",
@@ -11284,10 +11272,8 @@
       "integrity": "sha512-aWAgTW4MoSJzZPAicljkO1hsi1oKj/RRq/OJQh2PKI2UKL04c2Bs+MBOB+BBABHTXJpf9mCwHN7ANCvYsvY2sg==",
       "dev": true,
       "dependencies": {
-        "chokidar": "^3.4.1",
         "graceful-fs": "^4.1.2",
-        "neo-async": "^2.5.0",
-        "watchpack-chokidar2": "^2.0.0"
+        "neo-async": "^2.5.0"
       },
       "optionalDependencies": {
         "chokidar": "^3.4.1",
@@ -11371,7 +11357,6 @@
         "anymatch": "^2.0.0",
         "async-each": "^1.0.1",
         "braces": "^2.3.2",
-        "fsevents": "^1.2.7",
         "glob-parent": "^3.1.0",
         "inherits": "^2.0.3",
         "is-binary-path": "^1.0.0",