diff --git a/README.md b/README.md
index 09bc078..af48247 100644
--- a/README.md
+++ b/README.md
@@ -296,7 +296,7 @@ An `EventEmitter` instance that emits the following events:
 | `browser_connect` | `ws` | Browser connected |
 | `browser_disconnect` | `{}` | Browser disconnected |
 | `dom_ready` | `{ id, index, status, active, title, url, container }` | A tab finished loading |
-| `dom_load_fail` | `{ id }` | A tab failed to load |
+| `dom_load_fail` | `{ id, url, error }` | A tab failed to load (Network error, `<=400` code) |
 | `web_request` | `{ id, url, status, origin, type, method, container, headers }` | A request was sent |
 | `web_response` | `{ id, url, status, origin, type, method, container, body }` | A response was received |
 
diff --git a/ext/bg.js b/ext/bg.js
index dccd608..e6fb26c 100644
--- a/ext/bg.js
+++ b/ext/bg.js
@@ -15,7 +15,7 @@ var proxy_map = {};
 
 var web_response_whitelist = ["main_frame", "xmlhttprequest"];
 
-const log_debug = true;
+const log_debug = false;
 
 browser.browserAction.setBadgeBackgroundColor({
 	color: [0, 0, 0, 0]
@@ -638,16 +638,56 @@ browser.tabs.onUpdated.addListener(function(tabid, event, tab){
 	}
 });
 
+browser.webRequest.onHeadersReceived.addListener(function(page){
+		
+		if(page.type != "main_frame"){
+			
+			return
+		};
+		
+		// send error on 4xx code
+		if(page.statusCode >= 400){
+			
+			send_event(
+				global_ws,
+				{
+					"action": "dom_load_fail",
+					"data": {
+						id: page.tabId,
+						url: page.url,
+						error: page.statusLine.trim()
+					}
+				}
+			);
+		}
+	},
+	{ urls: ["<all_urls>"] }
+);
+
 browser.webNavigation.onErrorOccurred.addListener(function(page){
 	
-	if(connected === false){ return; }
+	if(
+		connected === false ||
+		// must be an error in parent frame
+		page.frameId !== 0 ||
+		// ignore HSTS error. See:
+		// https://bugzilla.mozilla.org/show_bug.cgi?id=1801326
+		page.error == "Error code 2152398850" ||
+		// page-load abort
+		page.error == "NS_BINDING_ABORTED"
+	){
+		
+		return;
+	}
 	
 	send_event(
 		global_ws,
 		{
 			"action": "dom_load_fail",
 			"data": {
-				id: page.tabId
+				id: page.tabId,
+				url: page.url,
+				error: page.error
 			}
 		}
 	);