diff --git a/lib/types/redux-types.js b/lib/types/redux-types.js
--- a/lib/types/redux-types.js
+++ b/lib/types/redux-types.js
@@ -1363,11 +1363,13 @@
     };
 
 export type ActionPayload = ?(Object | Array<*> | $ReadOnlyArray<*> | string);
+export type DispatchSource = 'tunnelbroker' | 'tab-sync';
 export type SuperAction = {
   type: string,
   payload?: ActionPayload,
   loadingInfo?: LoadingInfo,
   error?: boolean,
+  dispatchSource?: DispatchSource,
 };
 type ThunkedAction = (dispatch: Dispatch) => void;
 export type PromisedAction = (dispatch: Dispatch) => Promise<void>;
diff --git a/web/redux/redux-setup.js b/web/redux/redux-setup.js
--- a/web/redux/redux-setup.js
+++ b/web/redux/redux-setup.js
@@ -122,17 +122,17 @@
 
 export type Action =
   | BaseAction
-  | { type: 'UPDATE_NAV_INFO', payload: Partial<WebNavInfo> }
+  | { +type: 'UPDATE_NAV_INFO', +payload: Partial<WebNavInfo> }
   | {
-      type: 'UPDATE_WINDOW_DIMENSIONS',
-      payload: WindowDimensions,
+      +type: 'UPDATE_WINDOW_DIMENSIONS',
+      +payload: WindowDimensions,
     }
   | {
-      type: 'UPDATE_WINDOW_ACTIVE',
-      payload: boolean,
+      +type: 'UPDATE_WINDOW_ACTIVE',
+      +payload: boolean,
     }
-  | { +type: 'SET_CRYPTO_STORE', payload: CryptoStore }
-  | { +type: 'SET_INITIAL_REDUX_STATE', payload: InitialReduxState };
+  | { +type: 'SET_CRYPTO_STORE', +payload: CryptoStore }
+  | { +type: 'SET_INITIAL_REDUX_STATE', +payload: InitialReduxState };
 
 function reducer(oldState: AppState | void, action: Action): AppState {
   invariant(oldState, 'should be set');
@@ -162,6 +162,7 @@
       });
     }
     return validateStateAndProcessDBOperations(
+      action,
       oldState,
       {
         ...state,
@@ -183,6 +184,7 @@
     );
   } else if (action.type === updateWindowDimensionsActionType) {
     return validateStateAndProcessDBOperations(
+      action,
       oldState,
       {
         ...state,
@@ -192,6 +194,7 @@
     );
   } else if (action.type === updateWindowActiveActionType) {
     return validateStateAndProcessDBOperations(
+      action,
       oldState,
       {
         ...state,
@@ -340,10 +343,16 @@
     communityPickerStore,
   };
 
-  return validateStateAndProcessDBOperations(oldState, state, storeOperations);
+  return validateStateAndProcessDBOperations(
+    action,
+    oldState,
+    state,
+    storeOperations,
+  );
 }
 
 function validateStateAndProcessDBOperations(
+  action: Action,
   oldState: AppState,
   state: AppState,
   storeOperations: StoreOperations,
@@ -454,10 +463,19 @@
     };
   }
 
-  void processDBStoreOperations(
-    storeOperations,
-    state.currentUserInfo?.id ?? null,
-  );
+  // The operations were already dispatched from the main tab
+
+  // For now the `dispatchSource` field is not included in any of the
+  // redux actions and this causes flow to throw an error.
+  // As soon as one of the actions is updated, this fix (and the corresponding
+  // one in tab-synchronization.js) can be removed.
+  // $FlowFixMe
+  if (action.dispatchSource !== 'tab-sync') {
+    void processDBStoreOperations(
+      storeOperations,
+      state.currentUserInfo?.id ?? null,
+    );
+  }
 
   return state;
 }
diff --git a/web/redux/tab-synchronization.js b/web/redux/tab-synchronization.js
new file mode 100644
--- /dev/null
+++ b/web/redux/tab-synchronization.js
@@ -0,0 +1,36 @@
+// @flow
+
+import type { Middleware, Store } from 'redux';
+
+import type { Action, AppState } from './redux-setup.js';
+
+const WEB_REDUX_CHANNEL = new BroadcastChannel('shared-redux');
+
+const tabSynchronizationMiddleware: Middleware<AppState, Action> =
+  () => next => action => {
+    const result = next(action);
+    // For now the `dispatchSource` field is not included in any of the
+    // redux actions and this causes flow to throw an error.
+    // As soon as one of the actions is updated, this fix (and the corresponding
+    // one in redux-setup.js) can be removed.
+    // $FlowFixMe
+    if (action.dispatchSource === 'tunnelbroker') {
+      WEB_REDUX_CHANNEL.postMessage(action);
+    }
+    return result;
+  };
+
+function synchronizeStoreWithOtherTabs(store: Store<AppState, Action>) {
+  WEB_REDUX_CHANNEL.onmessage = event => {
+    // We can be sure that we only pass actions through the broadcast channel.
+    // Additionally we know that this is one of the actions that contains the
+    // `dispatchSource` field.
+    const action: Action = ({
+      ...event.data,
+      dispatchSource: 'tab-sync',
+    }: any);
+    store.dispatch(action);
+  };
+}
+
+export { tabSynchronizationMiddleware, synchronizeStoreWithOtherTabs };
diff --git a/web/root.js b/web/root.js
--- a/web/root.js
+++ b/web/root.js
@@ -27,6 +27,10 @@
 import InitialReduxStateGate from './redux/initial-state-gate.js';
 import { persistConfig } from './redux/persist.js';
 import { type AppState, type Action, reducer } from './redux/redux-setup.js';
+import {
+  synchronizeStoreWithOtherTabs,
+  tabSynchronizationMiddleware,
+} from './redux/tab-synchronization.js';
 import history from './router-history.js';
 import Socket from './socket.react.js';
 
@@ -36,8 +40,11 @@
 const store: Store<AppState, Action> = createStore(
   persistedReducer,
   defaultWebState,
-  composeWithDevTools({})(applyMiddleware(thunk, reduxLoggerMiddleware)),
+  composeWithDevTools({})(
+    applyMiddleware(thunk, reduxLoggerMiddleware, tabSynchronizationMiddleware),
+  ),
 );
+synchronizeStoreWithOtherTabs(store);
 const persistor = persistStore(store);
 
 const RootProvider = (): React.Node => (