From f6232676e0e44d005f1793a0ada0b1aa02af0f8a Mon Sep 17 00:00:00 2001
From: Adriaan van Rossum <1079135+adriaanvanrossum@users.noreply.github.com>
Date: Tue, 21 Apr 2026 16:20:34 +0200
Subject: [PATCH] Fix Chrome detection breaking onBeforeRequest listener

Recent Chrome MV3 versions expose a `browser` global alias, which caused
`IS_FIREFOX` to incorrectly evaluate to `true` in Chrome. The extension
then tried to register a blocking `chrome.webRequest.onBeforeRequest`
listener that doesn't exist in the Chrome MV3 manifest, throwing
"Cannot read properties of undefined (reading 'onBeforeRequest')".

Switch to feature-detecting `declarativeNetRequest` vs. blocking
`webRequest` so Chrome uses dynamic rules and Firefox keeps using
webRequest. Also guard `updateListeners` against a missing
`chrome.webRequest.onBeforeRequest` as a defensive fallback.
---
 background.js | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/background.js b/background.js
index c330202..669a395 100644
--- a/background.js
+++ b/background.js
@@ -4,9 +4,14 @@
 let blocklist = [];
 let tabs = {};
 
-// Detect if the extension is running in Firefox
+// Detect if the extension is running in Firefox.
+// Chrome (MV3) exposes `chrome.declarativeNetRequest` but no blocking
+// `chrome.webRequest`. Recent Chrome versions also expose a `browser` global,
+// so we can't rely on that. Feature-detect the APIs we actually need instead.
 const IS_FIREFOX =
-  typeof browser !== "undefined" && typeof browser.runtime !== "undefined";
+  typeof chrome.declarativeNetRequest === "undefined" &&
+  typeof chrome.webRequest !== "undefined" &&
+  typeof chrome.webRequest.onBeforeRequest !== "undefined";
 const DEBUG = false;
 
 const debug = (...messages) => {
@@ -214,6 +219,13 @@ function updateListeners(blocklistLocal) {
 
   if (IS_FIREFOX) {
     // Firefox: Use webRequest API
+    if (!chrome.webRequest || !chrome.webRequest.onBeforeRequest) {
+      console.warn(
+        "chrome.webRequest.onBeforeRequest is not available; skipping listener update."
+      );
+      return;
+    }
+
     const urls = blocklist.reduce((list, { enabled, scripts = [] }) => {
       if (!enabled) return list;
       const add = scripts