diff --git a/application/basilisk/components/webextensions/ext-tabs.js b/application/basilisk/components/webextensions/ext-tabs.js
index bb575aaabe..580282b934 100644
--- a/application/basilisk/components/webextensions/ext-tabs.js
+++ b/application/basilisk/components/webextensions/ext-tabs.js
@@ -77,6 +77,8 @@ extensions.on("page-shutdown", (type, context) => {
 
 extensions.on("fill-browser-data", (type, browser, data) => {
   data.tabId = browser ? TabManager.getBrowserId(browser) : -1;
+  data.windowId = browser && browser.ownerGlobal ? WindowManager.getId(browser.ownerGlobal) : -1;
+  data.incognito = !!(browser && PrivateBrowsingUtils.isBrowserPrivate(browser));
 });
 /* eslint-enable mozilla/balanced-listeners */
 
diff --git a/toolkit/components/webextensions/ext-webRequest.js b/toolkit/components/webextensions/ext-webRequest.js
index a1f38169ea..9f2e0c8540 100644
--- a/toolkit/components/webextensions/ext-webRequest.js
+++ b/toolkit/components/webextensions/ext-webRequest.js
@@ -48,10 +48,27 @@ function WebRequestEventManager(context, eventName) {
         data2.ip = data.ip;
       }
 
+      if ("incognito" in data) {
+        data2.incognito = data.incognito;
+      }
+
       extensions.emit("fill-browser-data", data.browser, data2);
 
+      if ("tabId" in filter && data2.tabId !== filter.tabId) {
+        return;
+      }
+
+      if ("windowId" in filter && data2.windowId !== filter.windowId) {
+        return;
+      }
+
+      if ("incognito" in filter && !!data2.incognito !== filter.incognito) {
+        return;
+      }
+
       let optional = ["requestHeaders", "responseHeaders", "statusCode", "statusLine", "error", "redirectUrl",
-                      "requestBody"];
+                      "requestBody", "documentUrl", "scheme", "realm", "isProxy", "challenger",
+                      "proxyInfo", "frameAncestors"];
       for (let opt of optional) {
         if (opt in data) {
           data2[opt] = data[opt];
@@ -66,12 +83,15 @@ function WebRequestEventManager(context, eventName) {
     if (filter.types) {
       filter2.types = filter.types;
     }
-    if (filter.tabId) {
+    if ("tabId" in filter) {
       filter2.tabId = filter.tabId;
     }
-    if (filter.windowId) {
+    if ("windowId" in filter) {
       filter2.windowId = filter.windowId;
     }
+    if ("incognito" in filter) {
+      filter2.incognito = filter.incognito;
+    }
 
     let info2 = [];
     if (info) {
@@ -96,42 +116,6 @@ function WebRequestEventManager(context, eventName) {
 
 WebRequestEventManager.prototype = Object.create(SingletonEventManager.prototype);
 
-// StreamFilter stub for response data filtering
-// Modern extensions may use filterResponseData(), we provide a basic stub
-function StreamFilterStub(requestId) {
-  this.requestId = requestId;
-  this.status = "unattached";
-  this.onstart = null;
-  this.ondata = null;
-  this.onstop = null;
-  this.onerror = null;
-}
-
-StreamFilterStub.prototype = {
-  write: function(data) {
-    // Stub: no-op - just accept the data without modification
-  },
-  close: function() {
-    this.status = "closed";
-    if (this.onstop) {
-      try {
-        this.onstop();
-      } catch (e) {}
-    }
-  },
-  error: function(error) {
-    this.status = "errored";
-    if (this.onerror) {
-      try {
-        this.onerror(error);
-      } catch (e) {}
-    }
-  },
-  disconnect: function() {
-    this.status = "closed";
-  }
-};
-
 extensions.registerSchemaAPI("webRequest", "addon_parent", context => {
   return {
     webRequest: {
@@ -145,6 +129,7 @@ extensions.registerSchemaAPI("webRequest", "addon_parent", context => {
       onCompleted: new WebRequestEventManager(context, "onCompleted").api(),
       handlerBehaviorChanged: function() {
         // TODO: Flush all caches.
+        return Promise.resolve();
       },
       // Resource type constants for feature detection and filtering
       ResourceType: Object.freeze({
@@ -168,11 +153,6 @@ extensions.registerSchemaAPI("webRequest", "addon_parent", context => {
         WEB_MANIFEST: "web_manifest",
         OTHER: "other"
       }),
-      // Stub implementation of filterResponseData for extensions that need it
-      // Returns a StreamFilter-like object that extensions can use to intercept responses
-      filterResponseData: function(requestId) {
-        return new StreamFilterStub(requestId);
-      },
       // Maximum handler behavior change calls per 10 minutes (per MDN spec)
       MAX_HANDLER_BEHAVIOR_CHANGED_CALLS_PER_10_MINUTES: 20,
     },
diff --git a/toolkit/modules/addons/WebRequest.jsm b/toolkit/modules/addons/WebRequest.jsm
index abb1ca04a3..39e77408ea 100644
--- a/toolkit/modules/addons/WebRequest.jsm
+++ b/toolkit/modules/addons/WebRequest.jsm
@@ -75,8 +75,13 @@ function parseFilter(filter) {
     filter = {};
   }
 
-  // FIXME: Support windowId filtering.
-  return {urls: filter.urls || null, types: filter.types || null};
+  return {
+    urls: filter.urls || null,
+    types: filter.types || null,
+    tabId: filter.tabId === undefined ? null : filter.tabId,
+    windowId: filter.windowId === undefined ? null : filter.windowId,
+    incognito: filter.incognito === undefined ? null : filter.incognito,
+  };
 }
 
 function parseExtra(extra, allowed = []) {