diff --git a/components/script/dom/dissimilaroriginwindow.rs b/components/script/dom/dissimilaroriginwindow.rs
index 70c384db822..b5af443a1a4 100644
--- a/components/script/dom/dissimilaroriginwindow.rs
+++ b/components/script/dom/dissimilaroriginwindow.rs
@@ -68,6 +68,7 @@ impl DissimilarOriginWindow {
                 global_to_clone_from.wgpu_id_hub(),
                 Some(global_to_clone_from.is_secure_context()),
                 false,
+                global_to_clone_from.is_online().clone(),
             ),
             window_proxy: Dom::from_ref(window_proxy),
             location: Default::default(),
diff --git a/components/script/dom/globalscope.rs b/components/script/dom/globalscope.rs
index ec2ed70dd15..1da3928831c 100644
--- a/components/script/dom/globalscope.rs
+++ b/components/script/dom/globalscope.rs
@@ -374,6 +374,11 @@ pub(crate) struct GlobalScope {
     #[ignore_malloc_size_of = "Rc<T> is hard"]
     notification_permission_request_callback_map:
         DomRefCell<HashMap<String, Rc<NotificationPermissionCallback>>>,
+
+    /// Switch offline and online events
+    #[no_trace]
+    #[ignore_malloc_size_of = "Arc<Mutex<bool>> does not implement MallocSizeOf"]
+    is_online: Arc<Mutex<bool>>,
 }
 
 /// A wrapper for glue-code between the ipc router and the event-loop.
@@ -735,6 +740,7 @@ impl GlobalScope {
         #[cfg(feature = "webgpu")] gpu_id_hub: Arc<IdentityHub>,
         inherited_secure_context: Option<bool>,
         unminify_js: bool,
+        is_online: Arc<Mutex<bool>>,
     ) -> Self {
         Self {
             task_manager: Default::default(),
@@ -779,6 +785,7 @@ impl GlobalScope {
             byte_length_queuing_strategy_size_function: OnceCell::new(),
             count_queuing_strategy_size_function: OnceCell::new(),
             notification_permission_request_callback_map: Default::default(),
+            is_online,
         }
     }
 
@@ -3444,6 +3451,10 @@ impl GlobalScope {
         unreachable!();
     }
 
+    pub(crate) fn is_online(&self) -> Arc<Mutex<bool>> {
+        self.is_online.clone()
+    }
+
     /// <https://www.w3.org/TR/CSP/#report-violation>
     #[allow(unsafe_code)]
     pub(crate) fn report_csp_violations(
diff --git a/components/script/dom/navigator.rs b/components/script/dom/navigator.rs
index ee67359f859..615ba80174d 100644
--- a/components/script/dom/navigator.rs
+++ b/components/script/dom/navigator.rs
@@ -224,7 +224,7 @@ impl NavigatorMethods<crate::DomTypeHolder> for Navigator {
 
     /// <https://html.spec.whatwg.org/multipage/#dom-navigator-online>
     fn OnLine(&self) -> bool {
-        true
+        *self.global().is_online().lock().unwrap()
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-navigator-plugins
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 24e694b4f06..c286f456132 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -398,6 +398,11 @@ pub(crate) struct Window {
 
     /// <https://dom.spec.whatwg.org/#window-current-event>
     current_event: DomRefCell<Option<Dom<Event>>>,
+
+    /// Switch offline and online events
+    #[no_trace]
+    #[ignore_malloc_size_of = "Arc<Mutex<bool>> does not implement MallocSizeOf"]
+    is_online: Arc<Mutex<bool>>,
 }
 
 impl Window {
@@ -3033,6 +3038,7 @@ impl Window {
         player_context: WindowGLContext,
         #[cfg(feature = "webgpu")] gpu_id_hub: Arc<IdentityHub>,
         inherited_secure_context: Option<bool>,
+        is_online: Arc<Mutex<bool>>,
     ) -> DomRoot<Self> {
         let error_reporter = CSSErrorReporter {
             pipelineid: pipeline_id,
@@ -3060,6 +3066,7 @@ impl Window {
                 gpu_id_hub,
                 inherited_secure_context,
                 unminify_js,
+                is_online,
             ),
             script_chan,
             layout: RefCell::new(layout),
@@ -3120,6 +3127,7 @@ impl Window {
             current_event: DomRefCell::new(None),
             theme: Cell::new(PrefersColorScheme::Light),
             trusted_types: Default::default(),
+            is_online: Arc::new(Mutex::new(true)),
         });
 
         unsafe {
diff --git a/components/script/dom/workerglobalscope.rs b/components/script/dom/workerglobalscope.rs
index fa94dcc1d04..a158a5b0c1e 100644
--- a/components/script/dom/workerglobalscope.rs
+++ b/components/script/dom/workerglobalscope.rs
@@ -5,8 +5,8 @@
 use std::cell::{RefCell, RefMut};
 use std::default::Default;
 use std::rc::Rc;
-use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
 use base::cross_process_instant::CrossProcessInstant;
@@ -174,6 +174,7 @@ impl WorkerGlobalScope {
                 gpu_id_hub,
                 init.inherited_secure_context,
                 false,
+                Arc::new(Mutex::new(true)),
             ),
             worker_id: init.worker_id,
             worker_name,
diff --git a/components/script/dom/workernavigator.rs b/components/script/dom/workernavigator.rs
index 0b0e90ffd0c..e3c7f290acc 100644
--- a/components/script/dom/workernavigator.rs
+++ b/components/script/dom/workernavigator.rs
@@ -107,7 +107,7 @@ impl WorkerNavigatorMethods<crate::DomTypeHolder> for WorkerNavigator {
 
     /// <https://html.spec.whatwg.org/multipage/#dom-navigator-online>
     fn OnLine(&self) -> bool {
-        true
+        *self.global().is_online().lock().unwrap()
     }
 
     // https://w3c.github.io/permissions/#navigator-and-workernavigator-extension
diff --git a/components/script/dom/workletglobalscope.rs b/components/script/dom/workletglobalscope.rs
index c478830ac0c..27337aa338c 100644
--- a/components/script/dom/workletglobalscope.rs
+++ b/components/script/dom/workletglobalscope.rs
@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
 
 use base::id::PipelineId;
 use constellation_traits::{ScriptToConstellationChan, ScriptToConstellationMessage};
@@ -110,6 +110,7 @@ impl WorkletGlobalScope {
                 init.gpu_id_hub.clone(),
                 init.inherited_secure_context,
                 false,
+                Arc::new(Mutex::new(true)),
             ),
             base_url,
             to_script_thread_sender: init.to_script_thread_sender.clone(),
diff --git a/components/script/messaging.rs b/components/script/messaging.rs
index 08d6fc841cf..9f9453305b8 100644
--- a/components/script/messaging.rs
+++ b/components/script/messaging.rs
@@ -92,6 +92,7 @@ impl MixedMessage {
                 ScriptThreadMessage::SetWebGPUPort(..) => None,
                 ScriptThreadMessage::SetScrollStates(id, ..) => Some(*id),
                 ScriptThreadMessage::EvaluateJavaScript(id, _, _) => Some(*id),
+                ScriptThreadMessage::SetNetWorkState(..) => None,
             },
             MixedMessage::FromScript(inner_msg) => match inner_msg {
                 MainThreadScriptMsg::Common(CommonScriptMsg::Task(_, _, pipeline_id, _)) => {
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index e0309298f3d..bc9095e67ec 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -23,8 +23,8 @@ use std::default::Default;
 use std::option::Option;
 use std::rc::Rc;
 use std::result::Result;
-use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Mutex};
 use std::thread;
 use std::time::{Duration, Instant, SystemTime};
 
@@ -128,6 +128,7 @@ use crate::dom::document::{
     Document, DocumentSource, FocusInitiator, HasBrowsingContext, IsHTMLDocument, TouchEventResult,
 };
 use crate::dom::element::Element;
+use crate::dom::eventtarget::EventTarget;
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::htmlanchorelement::HTMLAnchorElement;
 use crate::dom::htmliframeelement::HTMLIFrameElement;
@@ -336,6 +337,10 @@ pub struct ScriptThread {
     /// The screen coordinates where the primary mouse button was pressed.
     #[no_trace]
     relative_mouse_down_point: Cell<Point2D<f32, DevicePixel>>,
+
+    /// Switch offline and online events
+    #[no_trace]
+    is_online: Arc<Mutex<bool>>,
 }
 
 struct BHMExitSignal {
@@ -957,6 +962,7 @@ impl ScriptThread {
             inherited_secure_context: state.inherited_secure_context,
             layout_factory,
             relative_mouse_down_point: Cell::new(Point2D::zero()),
+            is_online: Arc::new(Mutex::new(true)),
         }
     }
 
@@ -1903,6 +1909,23 @@ impl ScriptThread {
             ScriptThreadMessage::EvaluateJavaScript(pipeline_id, evaluation_id, script) => {
                 self.handle_evaluate_javascript(pipeline_id, evaluation_id, script, can_gc);
             },
+            ScriptThreadMessage::SetNetWorkState(is_online) => {
+                self.handle_network_state(is_online, can_gc);
+            },
+        }
+    }
+
+    fn fire_network_events(&self, is_online: bool, can_gc: CanGc) {
+        let event_name = if is_online {
+            Atom::from("online")
+        } else {
+            Atom::from("offline")
+        };
+
+        for (_, document) in self.documents.borrow().iter() {
+            let window = document.window();
+            let event_target = window.upcast::<EventTarget>();
+            event_target.fire_event(event_name.clone(), can_gc);
         }
     }
 
@@ -3228,6 +3251,7 @@ impl ScriptThread {
             #[cfg(feature = "webgpu")]
             self.gpu_id_hub.clone(),
             incomplete.load_data.inherited_secure_context,
+            self.is_online.clone(),
         );
 
         let _realm = enter_realm(&*window);
@@ -3821,6 +3845,17 @@ impl ScriptThread {
         };
     }
 
+    fn handle_network_state(&self, is_online: bool, can_gc: CanGc) {
+        let mut online_lock = self.is_online.lock().unwrap();
+        let previous = *online_lock;
+        *online_lock = is_online;
+        drop(online_lock);
+
+        if previous != is_online {
+            self.fire_network_events(is_online, can_gc);
+        }
+    }
+
     pub(crate) fn enqueue_microtask(job: Microtask) {
         with_script_thread(|script_thread| {
             script_thread
diff --git a/components/shared/script/lib.rs b/components/shared/script/lib.rs
index 29acc51765c..d6c0531e6c3 100644
--- a/components/shared/script/lib.rs
+++ b/components/shared/script/lib.rs
@@ -248,6 +248,8 @@ pub enum ScriptThreadMessage {
     /// Evaluate the given JavaScript and return a result via a corresponding message
     /// to the Constellation.
     EvaluateJavaScript(PipelineId, JavaScriptEvaluationId, String),
+    /// Parameter indicates if online (true) or offline (false)
+    SetNetWorkState(bool),
 }
 
 impl fmt::Debug for ScriptThreadMessage {