4 files changed, 1050 insertions, 0 deletions
diff --git a/remote/cdp/observers/ChannelEventSink.sys.mjs b/remote/cdp/observers/ChannelEventSink.sys.mjs
new file mode 100644
index 0000000000..48e7c6ee64
--- /dev/null
+++ b/remote/cdp/observers/ChannelEventSink.sys.mjs
@@ -0,0 +1,100 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { ComponentUtils } from "resource://gre/modules/ComponentUtils.sys.mjs";
+
+const Cm = Components.manager;
+
+/**
+ * This is a nsIChannelEventSink implementation that monitors channel redirects.
+ * This has been forked from:
+ * https://searchfox.org/mozilla-central/source/devtools/server/actors/network-monitor/channel-event-sink.js
+ * The rest of this module is also more or less forking:
+ * https://searchfox.org/mozilla-central/source/devtools/server/actors/network-monitor/network-observer.js
+ * TODO(try to re-unify /remote/ with /devtools code)
+ */
+const SINK_CLASS_DESCRIPTION = "NetworkMonitor Channel Event Sink";
+const SINK_CLASS_ID = Components.ID("{c2b4c83e-607a-405a-beab-0ef5dbfb7617}");
+const SINK_CONTRACT_ID = "@mozilla.org/network/monitor/channeleventsink;1";
+const SINK_CATEGORY_NAME = "net-channel-event-sinks";
+
+function ChannelEventSink() {
+  this.wrappedJSObject = this;
+  this.collectors = new Set();
+}
+
+ChannelEventSink.prototype = {
+  QueryInterface: ChromeUtils.generateQI(["nsIChannelEventSink"]),
+
+  registerCollector(collector) {
+    this.collectors.add(collector);
+  },
+
+  unregisterCollector(collector) {
+    this.collectors.delete(collector);
+
+    if (this.collectors.size == 0) {
+      ChannelEventSinkFactory.unregister();
+    }
+  },
+
+  // eslint-disable-next-line no-shadow
+  asyncOnChannelRedirect(oldChannel, newChannel, flags, callback) {
+    for (const collector of this.collectors) {
+      try {
+        collector._onChannelRedirect(oldChannel, newChannel, flags);
+      } catch (ex) {
+        console.error(
+          "StackTraceCollector.onChannelRedirect threw an exception",
+          ex
+        );
+      }
+    }
+    callback.onRedirectVerifyCallback(Cr.NS_OK);
+  },
+};
+
+export const ChannelEventSinkFactory =
+  ComponentUtils.generateSingletonFactory(ChannelEventSink);
+
+ChannelEventSinkFactory.register = function () {
+  const registrar = Cm.QueryInterface(Ci.nsIComponentRegistrar);
+  if (registrar.isCIDRegistered(SINK_CLASS_ID)) {
+    return;
+  }
+
+  registrar.registerFactory(
+    SINK_CLASS_ID,
+    SINK_CLASS_DESCRIPTION,
+    SINK_CONTRACT_ID,
+    ChannelEventSinkFactory
+  );
+
+  Services.catMan.addCategoryEntry(
+    SINK_CATEGORY_NAME,
+    SINK_CONTRACT_ID,
+    SINK_CONTRACT_ID,
+    false,
+    true
+  );
+};
+
+ChannelEventSinkFactory.unregister = function () {
+  const registrar = Cm.QueryInterface(Ci.nsIComponentRegistrar);
+  registrar.unregisterFactory(SINK_CLASS_ID, ChannelEventSinkFactory);
+
+  Services.catMan.deleteCategoryEntry(
+    SINK_CATEGORY_NAME,
+    SINK_CONTRACT_ID,
+    false
+  );
+};
+
+ChannelEventSinkFactory.getService = function () {
+  // Make sure the ChannelEventSink service is registered before accessing it
+  ChannelEventSinkFactory.register();
+
+  return Cc[SINK_CONTRACT_ID].getService(Ci.nsIChannelEventSink)
+    .wrappedJSObject;
+};
diff --git a/remote/cdp/observers/ContextObserver.sys.mjs b/remote/cdp/observers/ContextObserver.sys.mjs
new file mode 100644
index 0000000000..d0d6fd1f93
--- /dev/null
+++ b/remote/cdp/observers/ContextObserver.sys.mjs
@@ -0,0 +1,178 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Helper class to coordinate Runtime and Page events.
+ * Events have to be sent in the following order:
+ *  - Runtime.executionContextDestroyed
+ *  - Page.frameNavigated
+ *  - Runtime.executionContextCreated
+ *
+ * This class also handles the special case of Pages going from/to the BF cache.
+ * When you navigate to a new URL, the previous document may be stored in the BF Cache.
+ * All its asynchronous operations are frozen (XHR, timeouts, ...) and a `pagehide` event
+ * is fired for this document. We then navigate to the new URL.
+ * If the user navigates back to the previous page, the page is resurected from the
+ * cache. A `pageshow` event is fired and its asynchronous operations are resumed.
+ *
+ * When a page is in the BF Cache, we should consider it as frozen and shouldn't try
+ * to execute any javascript. So that the ExecutionContext should be considered as
+ * being destroyed and the document navigated.
+ */
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  EventEmitter: "resource://gre/modules/EventEmitter.sys.mjs",
+
+  executeSoon: "chrome://remote/content/shared/Sync.sys.mjs",
+});
+
+export class ContextObserver {
+  constructor(chromeEventHandler) {
+    this.chromeEventHandler = chromeEventHandler;
+    lazy.EventEmitter.decorate(this);
+
+    this._fissionEnabled = Services.appinfo.fissionAutostart;
+
+    this.chromeEventHandler.addEventListener("DOMWindowCreated", this, {
+      mozSystemGroup: true,
+    });
+
+    // Listen for pageshow and pagehide to track pages going in/out to/from the BF Cache
+    this.chromeEventHandler.addEventListener("pageshow", this, {
+      mozSystemGroup: true,
+    });
+    this.chromeEventHandler.addEventListener("pagehide", this, {
+      mozSystemGroup: true,
+    });
+
+    Services.obs.addObserver(this, "document-element-inserted");
+    Services.obs.addObserver(this, "inner-window-destroyed");
+
+    // With Fission disabled the `DOMWindowCreated` event is fired too late.
+    // Use the `webnavigation-create` notification instead.
+    if (!this._fissionEnabled) {
+      Services.obs.addObserver(this, "webnavigation-create");
+    }
+    Services.obs.addObserver(this, "webnavigation-destroy");
+  }
+
+  destructor() {
+    this.chromeEventHandler.removeEventListener("DOMWindowCreated", this, {
+      mozSystemGroup: true,
+    });
+    this.chromeEventHandler.removeEventListener("pageshow", this, {
+      mozSystemGroup: true,
+    });
+    this.chromeEventHandler.removeEventListener("pagehide", this, {
+      mozSystemGroup: true,
+    });
+
+    Services.obs.removeObserver(this, "document-element-inserted");
+    Services.obs.removeObserver(this, "inner-window-destroyed");
+
+    if (!this._fissionEnabled) {
+      Services.obs.removeObserver(this, "webnavigation-create");
+    }
+    Services.obs.removeObserver(this, "webnavigation-destroy");
+  }
+
+  handleEvent({ type, target, persisted }) {
+    const window = target.defaultView;
+    const frameId = window.browsingContext.id;
+    const id = window.windowGlobalChild.innerWindowId;
+
+    switch (type) {
+      case "DOMWindowCreated":
+        // Do not pass `id` here as that's the new document ID instead of the old one
+        // that is destroyed. Instead, pass the frameId and let the listener figure out
+        // what ExecutionContext(s) to destroy.
+        this.emit("context-destroyed", { frameId });
+
+        // With Fission enabled the frame is attached early enough so that
+        // expected network requests and responses are handles afterward.
+        // Otherwise send the event when `webnavigation-create` is received.
+        if (this._fissionEnabled) {
+          this.emit("frame-attached", { frameId, window });
+        }
+
+        break;
+
+      case "pageshow":
+        // `persisted` is true when this is about a page being resurected from BF Cache
+        if (!persisted) {
+          return;
+        }
+        // XXX(ochameau) we might have to emit FrameNavigate here to properly handle BF Cache
+        // scenario in Page domain events
+        this.emit("context-created", { windowId: id, window });
+        this.emit("script-loaded", { windowId: id, window });
+        break;
+
+      case "pagehide":
+        // `persisted` is true when this is about a page being frozen into BF Cache
+        if (!persisted) {
+          return;
+        }
+        this.emit("context-destroyed", { windowId: id });
+        break;
+    }
+  }
+
+  observe(subject, topic, data) {
+    switch (topic) {
+      case "document-element-inserted":
+        const window = subject.defaultView;
+
+        // Ignore events without a window and those from other tabs
+        if (
+          !window ||
+          window.docShell.chromeEventHandler !== this.chromeEventHandler
+        ) {
+          return;
+        }
+
+        // Send when the document gets attached to the window, and its location
+        // is available.
+        this.emit("frame-navigated", {
+          frameId: window.browsingContext.id,
+          window,
+        });
+
+        const id = window.windowGlobalChild.innerWindowId;
+        this.emit("context-created", { windowId: id, window });
+        // Delay script-loaded to allow context cleanup to happen first
+        lazy.executeSoon(() => {
+          this.emit("script-loaded", { windowId: id, window });
+        });
+        break;
+      case "inner-window-destroyed":
+        const windowId = subject.QueryInterface(Ci.nsISupportsPRUint64).data;
+        this.emit("context-destroyed", { windowId });
+        break;
+      case "webnavigation-create":
+        subject.QueryInterface(Ci.nsIDocShell);
+        this.onDocShellCreated(subject);
+        break;
+      case "webnavigation-destroy":
+        subject.QueryInterface(Ci.nsIDocShell);
+        this.onDocShellDestroyed(subject);
+        break;
+    }
+  }
+
+  onDocShellCreated(docShell) {
+    this.emit("frame-attached", {
+      frameId: docShell.browsingContext.id,
+      window: docShell.browsingContext.window,
+    });
+  }
+
+  onDocShellDestroyed(docShell) {
+    this.emit("frame-detached", {
+      frameId: docShell.browsingContext.id,
+    });
+  }
+}
diff --git a/remote/cdp/observers/NetworkObserver.sys.mjs b/remote/cdp/observers/NetworkObserver.sys.mjs
new file mode 100644
index 0000000000..ffd8028ba7
--- /dev/null
+++ b/remote/cdp/observers/NetworkObserver.sys.mjs
@@ -0,0 +1,630 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  CommonUtils: "resource://services-common/utils.sys.mjs",
+  EventEmitter: "resource://gre/modules/EventEmitter.sys.mjs",
+  NetUtil: "resource://gre/modules/NetUtil.sys.mjs",
+
+  ChannelEventSinkFactory:
+    "chrome://remote/content/cdp/observers/ChannelEventSink.sys.mjs",
+});
+
+XPCOMUtils.defineLazyServiceGetter(
+  lazy,
+  "gActivityDistributor",
+  "@mozilla.org/network/http-activity-distributor;1",
+  "nsIHttpActivityDistributor"
+);
+
+const CC = Components.Constructor;
+
+ChromeUtils.defineLazyGetter(lazy, "BinaryInputStream", () => {
+  return CC(
+    "@mozilla.org/binaryinputstream;1",
+    "nsIBinaryInputStream",
+    "setInputStream"
+  );
+});
+
+ChromeUtils.defineLazyGetter(lazy, "BinaryOutputStream", () => {
+  return CC(
+    "@mozilla.org/binaryoutputstream;1",
+    "nsIBinaryOutputStream",
+    "setOutputStream"
+  );
+});
+
+ChromeUtils.defineLazyGetter(lazy, "StorageStream", () => {
+  return CC("@mozilla.org/storagestream;1", "nsIStorageStream", "init");
+});
+
+// Cap response storage with 100Mb per tracked tab.
+const MAX_RESPONSE_STORAGE_SIZE = 100 * 1024 * 1024;
+
+export class NetworkObserver {
+  constructor() {
+    lazy.EventEmitter.decorate(this);
+    this._browserSessionCount = new Map();
+    lazy.gActivityDistributor.addObserver(this);
+    lazy.ChannelEventSinkFactory.getService().registerCollector(this);
+
+    this._redirectMap = new Map();
+
+    // Request interception state.
+    this._browserSuspendedChannels = new Map();
+    this._extraHTTPHeaders = new Map();
+    this._browserResponseStorages = new Map();
+
+    this._onRequest = this._onRequest.bind(this);
+    this._onExamineResponse = this._onResponse.bind(
+      this,
+      false /* fromCache */
+    );
+    this._onCachedResponse = this._onResponse.bind(this, true /* fromCache */);
+  }
+
+  dispose() {
+    lazy.gActivityDistributor.removeObserver(this);
+    lazy.ChannelEventSinkFactory.getService().unregisterCollector(this);
+
+    Services.obs.removeObserver(this._onRequest, "http-on-modify-request");
+    Services.obs.removeObserver(
+      this._onExamineResponse,
+      "http-on-examine-response"
+    );
+    Services.obs.removeObserver(
+      this._onCachedResponse,
+      "http-on-examine-cached-response"
+    );
+    Services.obs.removeObserver(
+      this._onCachedResponse,
+      "http-on-examine-merged-response"
+    );
+  }
+
+  setExtraHTTPHeaders(browser, headers) {
+    if (!headers) {
+      this._extraHTTPHeaders.delete(browser);
+    } else {
+      this._extraHTTPHeaders.set(browser, headers);
+    }
+  }
+
+  enableRequestInterception(browser) {
+    if (!this._browserSuspendedChannels.has(browser)) {
+      this._browserSuspendedChannels.set(browser, new Map());
+    }
+  }
+
+  disableRequestInterception(browser) {
+    const suspendedChannels = this._browserSuspendedChannels.get(browser);
+    if (!suspendedChannels) {
+      return;
+    }
+    this._browserSuspendedChannels.delete(browser);
+    for (const channel of suspendedChannels.values()) {
+      channel.resume();
+    }
+  }
+
+  resumeSuspendedRequest(browser, requestId, headers) {
+    const suspendedChannels = this._browserSuspendedChannels.get(browser);
+    if (!suspendedChannels) {
+      throw new Error(`Request interception is not enabled`);
+    }
+    const httpChannel = suspendedChannels.get(requestId);
+    if (!httpChannel) {
+      throw new Error(`Cannot find request "${requestId}"`);
+    }
+    if (headers) {
+      // 1. Clear all previous headers.
+      for (const header of requestHeaders(httpChannel)) {
+        httpChannel.setRequestHeader(header.name, "", false /* merge */);
+      }
+      // 2. Set new headers.
+      for (const header of headers) {
+        httpChannel.setRequestHeader(
+          header.name,
+          header.value,
+          false /* merge */
+        );
+      }
+    }
+    suspendedChannels.delete(requestId);
+    httpChannel.resume();
+  }
+
+  getResponseBody(browser, requestId) {
+    const responseStorage = this._browserResponseStorages.get(browser);
+    if (!responseStorage) {
+      throw new Error("Responses are not tracked for the given browser");
+    }
+    return responseStorage.getBase64EncodedResponse(requestId);
+  }
+
+  abortSuspendedRequest(browser, aRequestId) {
+    const suspendedChannels = this._browserSuspendedChannels.get(browser);
+    if (!suspendedChannels) {
+      throw new Error(`Request interception is not enabled`);
+    }
+    const httpChannel = suspendedChannels.get(aRequestId);
+    if (!httpChannel) {
+      throw new Error(`Cannot find request "${aRequestId}"`);
+    }
+    suspendedChannels.delete(aRequestId);
+    httpChannel.cancel(Cr.NS_ERROR_FAILURE);
+    httpChannel.resume();
+    this.emit("requestfailed", httpChannel, {
+      requestId: requestId(httpChannel),
+      errorCode: getNetworkErrorStatusText(httpChannel.status),
+    });
+  }
+
+  _onChannelRedirect(oldChannel, newChannel) {
+    // We can be called with any nsIChannel, but are interested only in HTTP channels
+    try {
+      oldChannel.QueryInterface(Ci.nsIHttpChannel);
+      newChannel.QueryInterface(Ci.nsIHttpChannel);
+    } catch (ex) {
+      return;
+    }
+
+    const httpChannel = oldChannel.QueryInterface(Ci.nsIHttpChannel);
+    const loadContext = getLoadContext(httpChannel);
+    if (
+      !loadContext ||
+      !this._browserSessionCount.has(loadContext.topFrameElement)
+    ) {
+      return;
+    }
+    this._redirectMap.set(newChannel, oldChannel);
+  }
+
+  _onRequest(channel, topic) {
+    const httpChannel = channel.QueryInterface(Ci.nsIHttpChannel);
+    const loadContext = getLoadContext(httpChannel);
+    const browser = loadContext?.topFrameElement;
+    if (!loadContext || !this._browserSessionCount.has(browser)) {
+      return;
+    }
+
+    const extraHeaders = this._extraHTTPHeaders.get(browser);
+    if (extraHeaders) {
+      for (const header of extraHeaders) {
+        httpChannel.setRequestHeader(
+          header.name,
+          header.value,
+          false /* merge */
+        );
+      }
+    }
+    const causeType = httpChannel.loadInfo
+      ? httpChannel.loadInfo.externalContentPolicyType
+      : Ci.nsIContentPolicy.TYPE_OTHER;
+
+    const suspendedChannels = this._browserSuspendedChannels.get(browser);
+    if (suspendedChannels) {
+      httpChannel.suspend();
+      suspendedChannels.set(requestId(httpChannel), httpChannel);
+    }
+
+    const oldChannel = this._redirectMap.get(httpChannel);
+    this._redirectMap.delete(httpChannel);
+
+    // Install response body hooks.
+    new ResponseBodyListener(this, browser, httpChannel);
+
+    this.emit("request", httpChannel, {
+      url: httpChannel.URI.spec,
+      suspended: suspendedChannels ? true : undefined,
+      requestId: requestId(httpChannel),
+      redirectedFrom: oldChannel ? requestId(oldChannel) : undefined,
+      postData: readRequestPostData(httpChannel),
+      headers: requestHeaders(httpChannel),
+      method: httpChannel.requestMethod,
+      isNavigationRequest: httpChannel.isMainDocumentChannel,
+      cause: causeType,
+      causeString: causeTypeToString(causeType),
+      frameId: this.frameId(httpChannel),
+      // clients expect loaderId == requestId for document navigation
+      loaderId: [
+        Ci.nsIContentPolicy.TYPE_DOCUMENT,
+        Ci.nsIContentPolicy.TYPE_SUBDOCUMENT,
+      ].includes(causeType)
+        ? requestId(httpChannel)
+        : undefined,
+    });
+  }
+
+  _onResponse(fromCache, httpChannel, topic) {
+    const loadContext = getLoadContext(httpChannel);
+    if (
+      !loadContext ||
+      !this._browserSessionCount.has(loadContext.topFrameElement)
+    ) {
+      return;
+    }
+    httpChannel.QueryInterface(Ci.nsIHttpChannelInternal);
+    const causeType = httpChannel.loadInfo
+      ? httpChannel.loadInfo.externalContentPolicyType
+      : Ci.nsIContentPolicy.TYPE_OTHER;
+    let remoteIPAddress;
+    let remotePort;
+    try {
+      remoteIPAddress = httpChannel.remoteAddress;
+      remotePort = httpChannel.remotePort;
+    } catch (e) {
+      // remoteAddress is not defined for cached requests.
+    }
+
+    this.emit("response", httpChannel, {
+      requestId: requestId(httpChannel),
+      securityDetails: getSecurityDetails(httpChannel),
+      fromCache,
+      headers: responseHeaders(httpChannel),
+      requestHeaders: requestHeaders(httpChannel),
+      remoteIPAddress,
+      remotePort,
+      status: httpChannel.responseStatus,
+      statusText: httpChannel.responseStatusText,
+      cause: causeType,
+      causeString: causeTypeToString(causeType),
+      frameId: this.frameId(httpChannel),
+      // clients expect loaderId == requestId for document navigation
+      loaderId: [
+        Ci.nsIContentPolicy.TYPE_DOCUMENT,
+        Ci.nsIContentPolicy.TYPE_SUBDOCUMENT,
+      ].includes(causeType)
+        ? requestId(httpChannel)
+        : undefined,
+    });
+  }
+
+  _onResponseFinished(browser, httpChannel, body) {
+    const responseStorage = this._browserResponseStorages.get(browser);
+    if (!responseStorage) {
+      return;
+    }
+    responseStorage.addResponseBody(httpChannel, body);
+    this.emit("requestfinished", httpChannel, {
+      requestId: requestId(httpChannel),
+      errorCode: getNetworkErrorStatusText(httpChannel.status),
+    });
+  }
+
+  isActive(browser) {
+    return !!this._browserSessionCount.get(browser);
+  }
+
+  startTrackingBrowserNetwork(browser) {
+    const value = this._browserSessionCount.get(browser) || 0;
+    this._browserSessionCount.set(browser, value + 1);
+    if (value === 0) {
+      Services.obs.addObserver(this._onRequest, "http-on-modify-request");
+      Services.obs.addObserver(
+        this._onExamineResponse,
+        "http-on-examine-response"
+      );
+      Services.obs.addObserver(
+        this._onCachedResponse,
+        "http-on-examine-cached-response"
+      );
+      Services.obs.addObserver(
+        this._onCachedResponse,
+        "http-on-examine-merged-response"
+      );
+      this._browserResponseStorages.set(
+        browser,
+        new ResponseStorage(
+          MAX_RESPONSE_STORAGE_SIZE,
+          MAX_RESPONSE_STORAGE_SIZE / 10
+        )
+      );
+    }
+    return () => this.stopTrackingBrowserNetwork(browser);
+  }
+
+  stopTrackingBrowserNetwork(browser) {
+    const value = this._browserSessionCount.get(browser);
+    if (value) {
+      this._browserSessionCount.set(browser, value - 1);
+    } else {
+      this._browserSessionCount.delete(browser);
+      this._browserResponseStorages.delete(browser);
+      this.dispose();
+    }
+  }
+
+  /**
+   * Returns the frameId of the current httpChannel.
+   */
+  frameId(httpChannel) {
+    const loadInfo = httpChannel.loadInfo;
+    return loadInfo.frameBrowsingContext?.id || loadInfo.browsingContext.id;
+  }
+}
+
+const protocolVersionNames = {
+  [Ci.nsITransportSecurityInfo.TLS_VERSION_1]: "TLS 1",
+  [Ci.nsITransportSecurityInfo.TLS_VERSION_1_1]: "TLS 1.1",
+  [Ci.nsITransportSecurityInfo.TLS_VERSION_1_2]: "TLS 1.2",
+  [Ci.nsITransportSecurityInfo.TLS_VERSION_1_3]: "TLS 1.3",
+};
+
+function getSecurityDetails(httpChannel) {
+  const securityInfo = httpChannel.securityInfo;
+  if (!securityInfo) {
+    return null;
+  }
+  if (!securityInfo.serverCert) {
+    return null;
+  }
+  return {
+    protocol: protocolVersionNames[securityInfo.protocolVersion] || "<unknown>",
+    subjectName: securityInfo.serverCert.commonName,
+    issuer: securityInfo.serverCert.issuerCommonName,
+    // Convert to seconds.
+    validFrom: securityInfo.serverCert.validity.notBefore / 1000 / 1000,
+    validTo: securityInfo.serverCert.validity.notAfter / 1000 / 1000,
+  };
+}
+
+function readRequestPostData(httpChannel) {
+  if (!(httpChannel instanceof Ci.nsIUploadChannel)) {
+    return undefined;
+  }
+  const iStream = httpChannel.uploadStream;
+  if (!iStream) {
+    return undefined;
+  }
+  const isSeekableStream = iStream instanceof Ci.nsISeekableStream;
+
+  let prevOffset;
+  if (isSeekableStream) {
+    prevOffset = iStream.tell();
+    iStream.seek(Ci.nsISeekableStream.NS_SEEK_SET, 0);
+  }
+
+  // Read data from the stream.
+  let text;
+  try {
+    text = lazy.NetUtil.readInputStreamToString(iStream, iStream.available());
+    const converter = Cc[
+      "@mozilla.org/intl/scriptableunicodeconverter"
+    ].createInstance(Ci.nsIScriptableUnicodeConverter);
+    converter.charset = "UTF-8";
+    text = converter.ConvertToUnicode(text);
+  } catch (err) {
+    text = undefined;
+  }
+
+  // Seek locks the file, so seek to the beginning only if necko hasn"t
+  // read it yet, since necko doesn"t seek to 0 before reading (at lest
+  // not till 459384 is fixed).
+  if (isSeekableStream && prevOffset == 0) {
+    iStream.seek(Ci.nsISeekableStream.NS_SEEK_SET, 0);
+  }
+  return text;
+}
+
+function getLoadContext(httpChannel) {
+  let loadContext = null;
+  try {
+    if (httpChannel.notificationCallbacks) {
+      loadContext = httpChannel.notificationCallbacks.getInterface(
+        Ci.nsILoadContext
+      );
+    }
+  } catch (e) {}
+  try {
+    if (!loadContext && httpChannel.loadGroup) {
+      loadContext = httpChannel.loadGroup.notificationCallbacks.getInterface(
+        Ci.nsILoadContext
+      );
+    }
+  } catch (e) {}
+  return loadContext;
+}
+
+function requestId(httpChannel) {
+  return String(httpChannel.channelId);
+}
+
+function requestHeaders(httpChannel) {
+  const headers = [];
+  httpChannel.visitRequestHeaders({
+    visitHeader: (name, value) => headers.push({ name, value }),
+  });
+  return headers;
+}
+
+function responseHeaders(httpChannel) {
+  const headers = [];
+  httpChannel.visitResponseHeaders({
+    visitHeader: (name, value) => headers.push({ name, value }),
+  });
+  return headers;
+}
+
+function causeTypeToString(causeType) {
+  for (let key in Ci.nsIContentPolicy) {
+    if (Ci.nsIContentPolicy[key] === causeType) {
+      return key;
+    }
+  }
+  return "TYPE_OTHER";
+}
+
+class ResponseStorage {
+  constructor(maxTotalSize, maxResponseSize) {
+    this._totalSize = 0;
+    this._maxResponseSize = maxResponseSize;
+    this._maxTotalSize = maxTotalSize;
+    this._responses = new Map();
+  }
+
+  addResponseBody(httpChannel, body) {
+    if (body.length > this._maxResponseSize) {
+      this._responses.set(requestId, {
+        evicted: true,
+        body: "",
+      });
+      return;
+    }
+    let encodings = [];
+    if (
+      httpChannel instanceof Ci.nsIEncodedChannel &&
+      httpChannel.contentEncodings &&
+      !httpChannel.applyConversion
+    ) {
+      const encodingHeader = httpChannel.getResponseHeader("Content-Encoding");
+      encodings = encodingHeader.split(/\s*\t*,\s*\t*/);
+    }
+    this._responses.set(requestId(httpChannel), { body, encodings });
+    this._totalSize += body.length;
+    if (this._totalSize > this._maxTotalSize) {
+      for (let [, response] of this._responses) {
+        this._totalSize -= response.body.length;
+        response.body = "";
+        response.evicted = true;
+        if (this._totalSize < this._maxTotalSize) {
+          break;
+        }
+      }
+    }
+  }
+
+  getBase64EncodedResponse(requestId) {
+    const response = this._responses.get(requestId);
+    if (!response) {
+      throw new Error(`Request "${requestId}" is not found`);
+    }
+    if (response.evicted) {
+      return { base64body: "", evicted: true };
+    }
+    let result = response.body;
+    if (response.encodings && response.encodings.length) {
+      for (const encoding of response.encodings) {
+        result = lazy.CommonUtils.convertString(
+          result,
+          encoding,
+          "uncompressed"
+        );
+      }
+    }
+    return { base64body: btoa(result) };
+  }
+}
+
+class ResponseBodyListener {
+  constructor(networkObserver, browser, httpChannel) {
+    this._networkObserver = networkObserver;
+    this._browser = browser;
+    this._httpChannel = httpChannel;
+    this._chunks = [];
+    this.QueryInterface = ChromeUtils.generateQI(["nsIStreamListener"]);
+    httpChannel.QueryInterface(Ci.nsITraceableChannel);
+    this.originalListener = httpChannel.setNewListener(this);
+  }
+
+  onDataAvailable(aRequest, aInputStream, aOffset, aCount) {
+    const iStream = new lazy.BinaryInputStream(aInputStream);
+    const sStream = new lazy.StorageStream(8192, aCount, null);
+    const oStream = new lazy.BinaryOutputStream(sStream.getOutputStream(0));
+
+    // Copy received data as they come.
+    const data = iStream.readBytes(aCount);
+    this._chunks.push(data);
+
+    oStream.writeBytes(data, aCount);
+    this.originalListener.onDataAvailable(
+      aRequest,
+      sStream.newInputStream(0),
+      aOffset,
+      aCount
+    );
+  }
+
+  onStartRequest(aRequest) {
+    this.originalListener.onStartRequest(aRequest);
+  }
+
+  onStopRequest(aRequest, aStatusCode) {
+    this.originalListener.onStopRequest(aRequest, aStatusCode);
+    const body = this._chunks.join("");
+    delete this._chunks;
+    this._networkObserver._onResponseFinished(
+      this._browser,
+      this._httpChannel,
+      body
+    );
+  }
+}
+
+function getNetworkErrorStatusText(status) {
+  if (!status) {
+    return null;
+  }
+  for (const key of Object.keys(Cr)) {
+    if (Cr[key] === status) {
+      return key;
+    }
+  }
+  // Security module. The following is taken from
+  // https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/How_to_check_the_secruity_state_of_an_XMLHTTPRequest_over_SSL
+  if ((status & 0xff0000) === 0x5a0000) {
+    // NSS_SEC errors (happen below the base value because of negative vals)
+    if (
+      (status & 0xffff) <
+      Math.abs(Ci.nsINSSErrorsService.NSS_SEC_ERROR_BASE)
+    ) {
+      // The bases are actually negative, so in our positive numeric space, we
+      // need to subtract the base off our value.
+      const nssErr =
+        Math.abs(Ci.nsINSSErrorsService.NSS_SEC_ERROR_BASE) - (status & 0xffff);
+      switch (nssErr) {
+        case 11:
+          return "SEC_ERROR_EXPIRED_CERTIFICATE";
+        case 12:
+          return "SEC_ERROR_REVOKED_CERTIFICATE";
+        case 13:
+          return "SEC_ERROR_UNKNOWN_ISSUER";
+        case 20:
+          return "SEC_ERROR_UNTRUSTED_ISSUER";
+        case 21:
+          return "SEC_ERROR_UNTRUSTED_CERT";
+        case 36:
+          return "SEC_ERROR_CA_CERT_INVALID";
+        case 90:
+          return "SEC_ERROR_INADEQUATE_KEY_USAGE";
+        case 176:
+          return "SEC_ERROR_CERT_SIGNATURE_ALGORITHM_DISABLED";
+        default:
+          return "SEC_ERROR_UNKNOWN";
+      }
+    }
+    const sslErr =
+      Math.abs(Ci.nsINSSErrorsService.NSS_SSL_ERROR_BASE) - (status & 0xffff);
+    switch (sslErr) {
+      case 3:
+        return "SSL_ERROR_NO_CERTIFICATE";
+      case 4:
+        return "SSL_ERROR_BAD_CERTIFICATE";
+      case 8:
+        return "SSL_ERROR_UNSUPPORTED_CERTIFICATE_TYPE";
+      case 9:
+        return "SSL_ERROR_UNSUPPORTED_VERSION";
+      case 12:
+        return "SSL_ERROR_BAD_CERT_DOMAIN";
+      default:
+        return "SSL_ERROR_UNKNOWN";
+    }
+  }
+  return "<unknown error>";
+}
diff --git a/remote/cdp/observers/TargetObserver.sys.mjs b/remote/cdp/observers/TargetObserver.sys.mjs
new file mode 100644
index 0000000000..dfd9e2d9dc
--- /dev/null
+++ b/remote/cdp/observers/TargetObserver.sys.mjs
@@ -0,0 +1,142 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  EventEmitter: "resource://gre/modules/EventEmitter.sys.mjs",
+
+  EventPromise: "chrome://remote/content/shared/Sync.sys.mjs",
+});
+
+// TODO(ato):
+//
+// The DOM team is working on pulling browsing context related behaviour,
+// such as window and tab handling, out of product code and into the platform.
+// This will have implication for the remote agent,
+// and as the platform gains support for product-independent events
+// we can likely get rid of this entire module.
+
+/**
+ * Observe Firefox tabs as they open and close.
+ *
+ * "open" fires when a tab opens.
+ * "close" fires when a tab closes.
+ */
+export class TabObserver {
+  /**
+   * @param {boolean?} [false] registerExisting
+   *     Events will be fired for ChromeWIndows and their respective tabs
+   *     at the time when the observer is started.
+   */
+  constructor({ registerExisting = false } = {}) {
+    lazy.EventEmitter.decorate(this);
+
+    this.registerExisting = registerExisting;
+
+    this.onTabOpen = this.onTabOpen.bind(this);
+    this.onTabClose = this.onTabClose.bind(this);
+  }
+
+  async start() {
+    Services.wm.addListener(this);
+
+    if (this.registerExisting) {
+      // Start listening for events on already open windows
+      for (const win of Services.wm.getEnumerator("navigator:browser")) {
+        this._registerDOMWindow(win);
+      }
+    }
+  }
+
+  stop() {
+    Services.wm.removeListener(this);
+
+    // Stop listening for events on still opened windows
+    for (const win of Services.wm.getEnumerator("navigator:browser")) {
+      this._unregisterDOMWindow(win);
+    }
+  }
+
+  // Event emitters
+
+  onTabOpen({ target }) {
+    this.emit("open", target);
+  }
+
+  onTabClose({ target }) {
+    this.emit("close", target);
+  }
+
+  // Internal methods
+
+  _registerDOMWindow(win) {
+    for (const tab of win.gBrowser.tabs) {
+      // a missing linkedBrowser means the tab is still initialising,
+      // and a TabOpen event will fire once it is ready
+      if (!tab.linkedBrowser) {
+        continue;
+      }
+
+      this.onTabOpen({ target: tab });
+    }
+
+    win.gBrowser.tabContainer.addEventListener("TabOpen", this.onTabOpen);
+    win.gBrowser.tabContainer.addEventListener("TabClose", this.onTabClose);
+  }
+
+  _unregisterDOMWindow(win) {
+    for (const tab of win.gBrowser.tabs) {
+      // a missing linkedBrowser means the tab is still initialising
+      if (!tab.linkedBrowser) {
+        continue;
+      }
+
+      // Emulate custom "TabClose" events because that event is not
+      // fired for each of the tabs when the window closes.
+      this.onTabClose({ target: tab });
+    }
+
+    win.gBrowser.tabContainer.removeEventListener("TabOpen", this.onTabOpen);
+    win.gBrowser.tabContainer.removeEventListener("TabClose", this.onTabClose);
+  }
+
+  // nsIWindowMediatorListener
+
+  async onOpenWindow(xulWindow) {
+    const win = xulWindow.docShell.domWindow;
+
+    await new lazy.EventPromise(win, "load");
+
+    // Return early if it's not a browser window
+    if (
+      win.document.documentElement.getAttribute("windowtype") !=
+      "navigator:browser"
+    ) {
+      return;
+    }
+
+    this._registerDOMWindow(win);
+  }
+
+  onCloseWindow(xulWindow) {
+    const win = xulWindow.docShell.domWindow;
+
+    // Return early if it's not a browser window
+    if (
+      win.document.documentElement.getAttribute("windowtype") !=
+      "navigator:browser"
+    ) {
+      return;
+    }
+
+    this._unregisterDOMWindow(win);
+  }
+
+  // XPCOM
+
+  get QueryInterface() {
+    return ChromeUtils.generateQI(["nsIWindowMediatorListener"]);
+  }
+}