diff --git a/toolkit/components/extensions/ProxyScriptContext.jsm b/toolkit/components/extensions/ProxyScriptContext.jsm
index 8e2ea2ce5140..a9770eea24ba 100644
--- a/toolkit/components/extensions/ProxyScriptContext.jsm
+++ b/toolkit/components/extensions/ProxyScriptContext.jsm
@@ -258,12 +258,14 @@ class ProxyChannelFilter {
 
   // Copy from WebRequest.jsm with small changes.
   getRequestData(channel, extraData) {
+    let originAttributes = channel.loadInfo && channel.loadInfo.originAttributes;
     let data = {
       requestId: String(channel.id),
       url: channel.finalURL,
       method: channel.method,
       type: channel.type,
       fromCache: !!channel.fromCache,
+      incognito: originAttributes && originAttributes.privateBrowsingId > 0,
 
       originUrl: channel.originURL || undefined,
       documentUrl: channel.documentURL || undefined,
diff --git a/toolkit/components/extensions/parent/ext-webRequest.js b/toolkit/components/extensions/parent/ext-webRequest.js
index a3293c3bf235..b07dad8c2dc4 100644
--- a/toolkit/components/extensions/parent/ext-webRequest.js
+++ b/toolkit/components/extensions/parent/ext-webRequest.js
@@ -24,7 +24,9 @@ function registerEvent(extension, eventName, fire, filter, info, remoteTab = nul
 
     let event = data.serialize(eventName);
     event.tabId = browserData.tabId;
-
+    if (data.originAttributes) {
+      event.incognito = data.originAttributes.privateBrowsingId > 0;
+    }
     if (data.registerTraceableChannel) {
       // If this is a primed listener, no tabParent was passed in here,
       // but the convert() callback later in this function will be called
diff --git a/toolkit/components/extensions/schemas/proxy.json b/toolkit/components/extensions/schemas/proxy.json
index b1596de3648b..4ce910e5b0b7 100644
--- a/toolkit/components/extensions/schemas/proxy.json
+++ b/toolkit/components/extensions/schemas/proxy.json
@@ -147,6 +147,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
diff --git a/toolkit/components/extensions/schemas/web_request.json b/toolkit/components/extensions/schemas/web_request.json
index b6d7e311495d..f3c6b2893951 100644
--- a/toolkit/components/extensions/schemas/web_request.json
+++ b/toolkit/components/extensions/schemas/web_request.json
@@ -425,6 +425,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "requestBody": {
@@ -493,6 +494,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
@@ -538,6 +540,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
@@ -578,6 +581,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
@@ -625,6 +629,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
@@ -684,6 +689,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
@@ -728,6 +734,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
@@ -773,6 +780,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
@@ -817,6 +825,7 @@
               "method": {"type": "string", "description": "Standard HTTP method."},
               "frameId": {"type": "integer", "description": "The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (<code>type</code> is <code>main_frame</code> or <code>sub_frame</code>), <code>frameId</code> indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab."},
               "parentFrameId": {"type": "integer", "description": "ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists."},
+              "incognito": {"type": "boolean", "optional": true, "description": "True for private browsing requests."},
               "originUrl": {"type": "string", "optional": true, "description": "URL of the resource that triggered this request."},
               "documentUrl": {"type": "string", "optional": true, "description": "URL of the page into which the requested resource will be loaded."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab."},
diff --git a/toolkit/components/extensions/test/xpcshell/test_ext_webRequest_incognito.js b/toolkit/components/extensions/test/xpcshell/test_ext_webRequest_incognito.js
index 8762094836d8..f306350e4357 100644
--- a/toolkit/components/extensions/test/xpcshell/test_ext_webRequest_incognito.js
+++ b/toolkit/components/extensions/test/xpcshell/test_ext_webRequest_incognito.js
@@ -11,21 +11,41 @@ server.registerPathHandler("/dummy", (request, response) => {
 add_task(async function test_incognito_webrequest_access() {
   Services.prefs.setBoolPref("extensions.allowPrivateBrowsingByDefault", false);
 
-  // This extension will fail if it gets a request
+  let pb_extension = ExtensionTestUtils.loadExtension({
+    incognitoOverride: "spanning",
+    manifest: {
+      permissions: ["webRequest", "webRequestBlocking", "<all_urls>"],
+    },
+    background() {
+      browser.webRequest.onBeforeRequest.addListener(async (details) => {
+        browser.test.assertTrue(details.incognito, "incognito flag is set");
+        browser.test.notifyPass("webRequest.private");
+      }, {urls: ["<all_urls>"]}, ["blocking"]);
+    },
+  });
+  await pb_extension.startup();
+
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["webRequest", "webRequestBlocking", "<all_urls>"],
     },
     background() {
       browser.webRequest.onBeforeRequest.addListener(async (details) => {
-        browser.test.fail("webrequest received incognito request");
+        browser.test.assertFalse(details.incognito, "incognito flag is not set");
+        browser.test.notifyPass("webRequest");
       }, {urls: ["<all_urls>"]}, ["blocking"]);
     },
   });
+  // Load non-incognito extension to check that private requests are invisible to it.
   await extension.startup();
 
   let contentPage = await ExtensionTestUtils.loadContentPage("http://example.com/dummy", {privateBrowsing: true});
+  await pb_extension.awaitFinish("webRequest.private");
+  await pb_extension.unload();
+  await contentPage.close();
 
+  contentPage = await ExtensionTestUtils.loadContentPage("http://example.com/dummy");
+  await extension.awaitFinish("webRequest");
   await extension.unload();
   await contentPage.close();
 
diff --git a/toolkit/components/extensions/test/xpcshell/test_proxy_incognito.js b/toolkit/components/extensions/test/xpcshell/test_proxy_incognito.js
index 072643605fcc..b7df6b2205f8 100644
--- a/toolkit/components/extensions/test/xpcshell/test_proxy_incognito.js
+++ b/toolkit/components/extensions/test/xpcshell/test_proxy_incognito.js
@@ -18,14 +18,15 @@ add_task(async function test_incognito_proxy_onRequest_access() {
   // extension does not have permission.
   Services.prefs.setBoolPref("extensions.allowPrivateBrowsingByDefault", false);
 
-  // This extension will fail if it gets a request
+  // This extension will fail if it gets a private request.
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
       permissions: ["proxy", "<all_urls>"],
     },
     async background() {
       browser.proxy.onRequest.addListener(async (details) => {
-        browser.test.fail("proxy.onRequest received incognito request");
+        browser.test.assertFalse(details.incognito, "incognito flag is not set");
+        browser.test.notifyPass("proxy.onRequest");
       }, {urls: ["<all_urls>"]});
 
       // Actual call arguments do not matter here.
@@ -42,7 +43,6 @@ add_task(async function test_incognito_proxy_onRequest_access() {
   await extension.startup();
   await extension.awaitMessage("ready");
 
-  // This extension will succeed if it gets a request
   let pextension = ExtensionTestUtils.loadExtension({
     incognitoOverride: "spanning",
     manifest: {
@@ -50,18 +50,22 @@ add_task(async function test_incognito_proxy_onRequest_access() {
     },
     background() {
       browser.proxy.onRequest.addListener(async (details) => {
-        browser.test.notifyPass("proxy.onRequest");
+        browser.test.assertTrue(details.incognito, "incognito flag is set");
+        browser.test.notifyPass("proxy.onRequest.private");
       }, {urls: ["<all_urls>"]});
     },
   });
   await pextension.startup();
 
-  let finished = pextension.awaitFinish("proxy.onRequest");
   let contentPage = await ExtensionTestUtils.loadContentPage("http://example.com/dummy", {privateBrowsing: true});
-  await finished;
+  await pextension.awaitFinish("proxy.onRequest.private");
+  await pextension.unload();
+  await contentPage.close();
+
+  contentPage = await ExtensionTestUtils.loadContentPage("http://example.com/dummy");
+  await extension.awaitFinish("proxy.onRequest");
 
   await extension.unload();
-  await pextension.unload();
   await contentPage.close();
 
   Services.prefs.clearUserPref("extensions.allowPrivateBrowsingByDefault");
diff --git a/toolkit/modules/addons/WebRequest.jsm b/toolkit/modules/addons/WebRequest.jsm
index bed5d06fd5e4..4022fd892b87 100644
--- a/toolkit/modules/addons/WebRequest.jsm
+++ b/toolkit/modules/addons/WebRequest.jsm
@@ -664,6 +664,7 @@ HttpObserverManager = {
   },
 
   getRequestData(channel, extraData) {
+    let originAttributes = channel.loadInfo && channel.loadInfo.originAttributes;
     let data = {
       requestId: String(channel.id),
       url: channel.finalURL,
@@ -671,6 +672,7 @@ HttpObserverManager = {
       browser: channel.browserElement,
       type: channel.type,
       fromCache: channel.fromCache,
+      originAttributes,
 
       originUrl: channel.originURL || undefined,
       documentUrl: channel.documentURL || undefined,