diff --git content/browser/devtools/devtools_http_handler.cc content/browser/devtools/devtools_http_handler.cc
index b75e19e7946b0..a92a7da426081 100644
--- content/browser/devtools/devtools_http_handler.cc
+++ content/browser/devtools/devtools_http_handler.cc
@@ -587,7 +587,7 @@ void DevToolsHttpHandler::OnJsonRequest(
     version.SetString("Protocol-Version",
                       DevToolsAgentHost::GetProtocolVersion());
     version.SetString("WebKit-Version", GetWebKitVersion());
-    version.SetString("Browser", GetContentClient()->browser()->GetProduct());
+    version.SetString("Browser", GetContentClient()->browser()->GetChromeProduct());
     version.SetString("User-Agent",
                       GetContentClient()->browser()->GetUserAgent());
     version.SetString("V8-Version", V8_VERSION_STRING);
diff --git content/browser/loader/navigation_url_loader_impl.cc content/browser/loader/navigation_url_loader_impl.cc
index 2bf604ee300d9..ded4a09961381 100644
--- content/browser/loader/navigation_url_loader_impl.cc
+++ content/browser/loader/navigation_url_loader_impl.cc
@@ -691,6 +691,17 @@ NavigationURLLoaderImpl::PrepareForNonInterceptedRequest(
           resource_request_->has_user_gesture, initiating_origin,
           initiator_document_.AsRenderFrameHostIfValid(), &loader_factory);
 
+      if (!handled) {
+        handled = GetContentClient()->browser()->HandleExternalProtocol(
+            web_contents_getter_, frame_tree_node_id_,
+            navigation_ui_data_.get(), request_info_->is_primary_main_frame,
+            FrameTreeNode::GloballyFindByID(frame_tree_node_id_)
+                ->IsInFencedFrameTree(),
+            request_info_->sandbox_flags,
+            *resource_request_, initiating_origin,
+            initiator_document_.AsRenderFrameHostIfValid(), &loader_factory);
+      }
+
       if (loader_factory) {
         factory = base::MakeRefCounted<network::WrapperSharedURLLoaderFactory>(
             std::move(loader_factory));
diff --git content/public/browser/content_browser_client.cc content/public/browser/content_browser_client.cc
index 69bcd725d0f86..a8456b3e8a941 100644
--- content/public/browser/content_browser_client.cc
+++ content/public/browser/content_browser_client.cc
@@ -9,7 +9,7 @@
 // declarations instead of including more headers. If that is infeasible, adjust
 // the limit. For more info, see
 // https://chromium.googlesource.com/chromium/src/+/HEAD/docs/wmax_tokens.md
-#pragma clang max_tokens_here 880000
+// #pragma clang max_tokens_here 880000
 
 #include <utility>
 
@@ -916,7 +916,7 @@ ContentBrowserClient::CreateURLLoaderHandlerForServiceWorkerNavigationPreload(
 void ContentBrowserClient::OnNetworkServiceCreated(
     network::mojom::NetworkService* network_service) {}
 
-void ContentBrowserClient::ConfigureNetworkContextParams(
+bool ContentBrowserClient::ConfigureNetworkContextParams(
     BrowserContext* context,
     bool in_memory,
     const base::FilePath& relative_partition_path,
@@ -925,6 +925,7 @@ void ContentBrowserClient::ConfigureNetworkContextParams(
         cert_verifier_creation_params) {
   network_context_params->user_agent = GetUserAgentBasedOnPolicy(context);
   network_context_params->accept_language = "en-us,en";
+  return true;
 }
 
 std::vector<base::FilePath>
diff --git content/public/browser/content_browser_client.h content/public/browser/content_browser_client.h
index d0b7aed3162b8..c494e9618d9dc 100644
--- content/public/browser/content_browser_client.h
+++ content/public/browser/content_browser_client.h
@@ -33,6 +33,7 @@
 #include "content/public/browser/login_delegate.h"
 #include "content/public/browser/mojo_binder_policy_map.h"
 #include "content/public/browser/storage_partition_config.h"
+#include "content/public/browser/web_contents.h"
 #include "content/public/common/alternative_error_page_override_info.mojom-forward.h"
 #include "content/public/common/page_visibility_state.h"
 #include "content/public/common/window_container_type.mojom-forward.h"
@@ -1690,7 +1691,7 @@ class CONTENT_EXPORT ContentBrowserClient {
   //
   // If |relative_partition_path| is the empty string, it means this needs to
   // create the default NetworkContext for the BrowserContext.
-  virtual void ConfigureNetworkContextParams(
+  virtual bool ConfigureNetworkContextParams(
       BrowserContext* context,
       bool in_memory,
       const base::FilePath& relative_partition_path,
@@ -1897,6 +1898,19 @@ class CONTENT_EXPORT ContentBrowserClient {
       RenderFrameHost* initiator_document,
       mojo::PendingRemote<network::mojom::URLLoaderFactory>* out_factory);
 
+  // Same as above, but exposing the whole ResourceRequest object.
+  virtual bool HandleExternalProtocol(
+      WebContents::Getter web_contents_getter,
+      int frame_tree_node_id,
+      NavigationUIData* navigation_data,
+      bool is_primary_main_frame,
+      bool is_in_fenced_frame_tree,
+      network::mojom::WebSandboxFlags sandbox_flags,
+      const network::ResourceRequest& request,
+      const absl::optional<url::Origin>& initiating_origin,
+      RenderFrameHost* initiator_document,
+      mojo::PendingRemote<network::mojom::URLLoaderFactory>* out_factory) { return false; }
+
   // Creates an OverlayWindow to be used for video or document
   // Picture-in-Picture respectively. This window will house the content shown
   // when in Picture-in-Picture mode. This will return a new OverlayWindow.
@@ -1958,6 +1972,10 @@ class CONTENT_EXPORT ContentBrowserClient {
   // Used as part of the user agent string.
   virtual std::string GetProduct();
 
+  // Returns the Chrome-specific product string. This is used for compatibility
+  // purposes with external tools like Selenium.
+  virtual std::string GetChromeProduct() { return GetProduct(); }
+
   // Returns the user agent. This can also return the reduced user agent, based
   // on blink::features::kUserAgentReduction. Content may cache this value.
   virtual std::string GetUserAgent();
diff --git content/public/renderer/content_renderer_client.h content/public/renderer/content_renderer_client.h
index 1dfe162dc69f4..93ece5d24f60f 100644
--- content/public/renderer/content_renderer_client.h
+++ content/public/renderer/content_renderer_client.h
@@ -92,6 +92,9 @@ class CONTENT_EXPORT ContentRendererClient {
   // binding requests from RenderProcessHost::BindReceiver().
   virtual void ExposeInterfacesToBrowser(mojo::BinderMap* binders) {}
 
+  // Notifies that the RenderThread can now send sync IPC messages.
+  virtual void RenderThreadConnected() {}
+
   // Notifies that a new RenderFrame has been created.
   virtual void RenderFrameCreated(RenderFrame* render_frame) {}
 
@@ -302,6 +305,10 @@ class CONTENT_EXPORT ContentRendererClient {
   // This method may invalidate the frame.
   virtual void RunScriptsAtDocumentIdle(RenderFrame* render_frame) {}
 
+  // Notifies that a DevTools agent has attached or detached.
+  virtual void DevToolsAgentAttached() {}
+  virtual void DevToolsAgentDetached() {}
+
   // Allows subclasses to enable some runtime features before Blink has
   // started.
   virtual void SetRuntimeFeaturesDefaultsBeforeBlinkInitialization() {}
diff --git content/renderer/render_thread_impl.cc content/renderer/render_thread_impl.cc
index ab74207b348f2..5cdda5796723f 100644
--- content/renderer/render_thread_impl.cc
+++ content/renderer/render_thread_impl.cc
@@ -609,6 +609,8 @@ void RenderThreadImpl::Init() {
       GetContentClient()->renderer()->CreateURLLoaderThrottleProvider(
           blink::URLLoaderThrottleProviderType::kFrame);
 
+  GetContentClient()->renderer()->RenderThreadConnected();
+
   GetAssociatedInterfaceRegistry()->AddInterface(base::BindRepeating(
       &RenderThreadImpl::OnRendererInterfaceReceiver, base::Unretained(this)));
 
diff --git content/renderer/renderer_blink_platform_impl.cc content/renderer/renderer_blink_platform_impl.cc
index 51ab896732604..8902f5d486ab9 100644
--- content/renderer/renderer_blink_platform_impl.cc
+++ content/renderer/renderer_blink_platform_impl.cc
@@ -1059,6 +1059,15 @@ SkBitmap* RendererBlinkPlatformImpl::GetSadPageBitmap() {
 
 //------------------------------------------------------------------------------
 
+void RendererBlinkPlatformImpl::DevToolsAgentAttached() {
+  GetContentClient()->renderer()->DevToolsAgentAttached();
+}
+void RendererBlinkPlatformImpl::DevToolsAgentDetached() {
+  GetContentClient()->renderer()->DevToolsAgentDetached();
+}
+
+//------------------------------------------------------------------------------
+
 std::unique_ptr<blink::WebV8ValueConverter>
 RendererBlinkPlatformImpl::CreateWebV8ValueConverter() {
   return std::make_unique<V8ValueConverterImpl>();
diff --git content/renderer/renderer_blink_platform_impl.h content/renderer/renderer_blink_platform_impl.h
index 156fb6cda9c41..17ca9be1f7e91 100644
--- content/renderer/renderer_blink_platform_impl.h
+++ content/renderer/renderer_blink_platform_impl.h
@@ -243,6 +243,9 @@ class CONTENT_EXPORT RendererBlinkPlatformImpl : public BlinkPlatformImpl {
       blink::WebVector<blink::WebContentSecurityPolicyHeader>* csp) override;
   base::PlatformThreadId GetIOThreadId() const override;
 
+  void DevToolsAgentAttached() override;
+  void DevToolsAgentDetached() override;
+
   // Tells this platform that the renderer is locked to a site (i.e., a scheme
   // plus eTLD+1, such as https://google.com), or to a more specific origin.
   void SetIsLockedToSite();