Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

42 files changed, 6341 insertions, 0 deletions

diff --git a/devtools/shared/commands/target/actions/moz.build b/devtools/shared/commands/target/actions/moz.build
new file mode 100644
index 0000000000..e9429c1200
--- /dev/null
+++ b/devtools/shared/commands/target/actions/moz.build
@@ -0,0 +1,7 @@
+# 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/.
+
+DevToolsModules(
+    "targets.js",
+)
diff --git a/devtools/shared/commands/target/actions/targets.js b/devtools/shared/commands/target/actions/targets.js
new file mode 100644
index 0000000000..577e5fedd3
--- /dev/null
+++ b/devtools/shared/commands/target/actions/targets.js
@@ -0,0 +1,33 @@
+/* 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/>. */
+"use strict";
+
+function registerTarget(targetFront) {
+  return { type: "REGISTER_TARGET", targetFront };
+}
+
+function unregisterTarget(targetFront) {
+  return { type: "UNREGISTER_TARGET", targetFront };
+}
+
+/**
+ *
+ * @param {String} targetActorID: The actorID of the target we want to select.
+ */
+function selectTarget(targetActorID) {
+  return function ({ dispatch, getState }) {
+    dispatch({ type: "SELECT_TARGET", targetActorID });
+  };
+}
+
+function refreshTargets() {
+  return { type: "REFRESH_TARGETS" };
+}
+
+module.exports = {
+  registerTarget,
+  unregisterTarget,
+  selectTarget,
+  refreshTargets,
+};
diff --git a/devtools/shared/commands/target/legacy-target-watchers/legacy-processes-watcher.js b/devtools/shared/commands/target/legacy-target-watchers/legacy-processes-watcher.js
new file mode 100644
index 0000000000..e0c5b18d51
--- /dev/null
+++ b/devtools/shared/commands/target/legacy-target-watchers/legacy-processes-watcher.js
@@ -0,0 +1,72 @@
+/* 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/. */
+
+"use strict";
+
+class LegacyProcessesWatcher {
+  constructor(targetCommand, onTargetAvailable, onTargetDestroyed) {
+    this.targetCommand = targetCommand;
+    this.rootFront = targetCommand.rootFront;
+
+    this.onTargetAvailable = onTargetAvailable;
+    this.onTargetDestroyed = onTargetDestroyed;
+
+    this.descriptors = new Set();
+    this._processListChanged = this._processListChanged.bind(this);
+  }
+
+  async _processListChanged() {
+    if (this.targetCommand.isDestroyed()) {
+      return;
+    }
+
+    const processes = await this.rootFront.listProcesses();
+    // Process the new list to detect the ones being destroyed
+    // Force destroyed the descriptor as well as the target
+    for (const descriptor of this.descriptors) {
+      if (!processes.includes(descriptor)) {
+        // Manually call onTargetDestroyed listeners in order to
+        // ensure calling them *before* destroying the descriptor.
+        // Otherwise the descriptor will automatically destroy the target
+        // and may not fire the contentProcessTarget's destroy event.
+        const target = descriptor.getCachedTarget();
+        if (target) {
+          this.onTargetDestroyed(target);
+        }
+
+        descriptor.destroy();
+        this.descriptors.delete(descriptor);
+      }
+    }
+
+    const promises = processes
+      .filter(descriptor => !this.descriptors.has(descriptor))
+      .map(async descriptor => {
+        // Add the new process descriptors to the local list
+        this.descriptors.add(descriptor);
+        const target = await descriptor.getTarget();
+        if (!target) {
+          console.error(
+            "Wasn't able to retrieve the target for",
+            descriptor.actorID
+          );
+          return;
+        }
+        await this.onTargetAvailable(target);
+      });
+
+    await Promise.all(promises);
+  }
+
+  async listen() {
+    this.rootFront.on("processListChanged", this._processListChanged);
+    await this._processListChanged();
+  }
+
+  unlisten() {
+    this.rootFront.off("processListChanged", this._processListChanged);
+  }
+}
+
+module.exports = LegacyProcessesWatcher;
diff --git a/devtools/shared/commands/target/legacy-target-watchers/legacy-serviceworkers-watcher.js b/devtools/shared/commands/target/legacy-target-watchers/legacy-serviceworkers-watcher.js
new file mode 100644
index 0000000000..adaeb9def4
--- /dev/null
+++ b/devtools/shared/commands/target/legacy-target-watchers/legacy-serviceworkers-watcher.js
@@ -0,0 +1,316 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  WorkersListener,
+  // eslint-disable-next-line mozilla/reject-some-requires
+} = require("resource://devtools/client/shared/workers-listener.js");
+
+const LegacyWorkersWatcher = require("resource://devtools/shared/commands/target/legacy-target-watchers/legacy-workers-watcher.js");
+
+class LegacyServiceWorkersWatcher extends LegacyWorkersWatcher {
+  // Holds the current target URL object
+  #currentTargetURL;
+
+  constructor(targetCommand, onTargetAvailable, onTargetDestroyed, commands) {
+    super(targetCommand, onTargetAvailable, onTargetDestroyed);
+    this._registrations = [];
+    this._processTargets = new Set();
+    this.commands = commands;
+
+    // We need to listen for registration changes at least in order to properly
+    // filter service workers by domain when debugging a local tab.
+    //
+    // A WorkerTarget instance has a url property, but it points to the url of
+    // the script, whereas the url property of the ServiceWorkerRegistration
+    // points to the URL controlled by the service worker.
+    //
+    // Historically we have been matching the service worker registration URL
+    // to match service workers for local tab tools (app panel & debugger).
+    // Maybe here we could have some more info on the actual worker.
+    this._workersListener = new WorkersListener(this.rootFront, {
+      registrationsOnly: true,
+    });
+
+    // Note that this is called much more often than when a registration
+    // is created or destroyed. WorkersListener notifies of anything that
+    // potentially impacted workers.
+    // I use it as a shortcut in this first patch. Listening to rootFront's
+    // "serviceWorkerRegistrationListChanged" should be enough to be notified
+    // about registrations. And if we need to also update the
+    // "debuggerServiceWorkerStatus" from here, then we would have to
+    // also listen to "registration-changed" one each registration.
+    this._onRegistrationListChanged =
+      this._onRegistrationListChanged.bind(this);
+    this._onDocumentEvent = this._onDocumentEvent.bind(this);
+
+    // Flag used from the parent class to listen to process targets.
+    // Decision tree is complicated, keep all logic in the parent methods.
+    this._isServiceWorkerWatcher = true;
+  }
+
+  /**
+   * Override from LegacyWorkersWatcher.
+   *
+   * We record all valid service worker targets (ie workers that match a service
+   * worker registration), but we will only notify about the ones which match
+   * the current domain.
+   */
+  _recordWorkerTarget(workerTarget) {
+    return !!this._getRegistrationForWorkerTarget(workerTarget);
+  }
+
+  // Override from LegacyWorkersWatcher.
+  _supportWorkerTarget(workerTarget) {
+    if (!workerTarget.isServiceWorker) {
+      return false;
+    }
+
+    const registration = this._getRegistrationForWorkerTarget(workerTarget);
+    return registration && this._isRegistrationValidForTarget(registration);
+  }
+
+  // Override from LegacyWorkersWatcher.
+  async listen() {
+    // Listen to the current target front.
+    this.target = this.targetCommand.targetFront;
+
+    if (this.targetCommand.descriptorFront.isTabDescriptor) {
+      this.#currentTargetURL = new URL(this.targetCommand.targetFront.url);
+    }
+
+    this._workersListener.addListener(this._onRegistrationListChanged);
+
+    // Fetch the registrations before calling listen, since service workers
+    // might already be available and will need to be compared with the existing
+    // registrations.
+    await this._onRegistrationListChanged();
+
+    if (this.targetCommand.descriptorFront.isTabDescriptor) {
+      await this.commands.resourceCommand.watchResources(
+        [this.commands.resourceCommand.TYPES.DOCUMENT_EVENT],
+        {
+          onAvailable: this._onDocumentEvent,
+          ignoreExistingResources: true,
+        }
+      );
+    }
+
+    await super.listen();
+  }
+
+  // Override from LegacyWorkersWatcher.
+  unlisten(...args) {
+    this._workersListener.removeListener(this._onRegistrationListChanged);
+
+    if (this.targetCommand.descriptorFront.isTabDescriptor) {
+      this.commands.resourceCommand.unwatchResources(
+        [this.commands.resourceCommand.TYPES.DOCUMENT_EVENT],
+        {
+          onAvailable: this._onDocumentEvent,
+        }
+      );
+    }
+
+    super.unlisten(...args);
+  }
+
+  // Override from LegacyWorkersWatcher.
+  async _onProcessAvailable({ targetFront }) {
+    if (this.targetCommand.descriptorFront.isTabDescriptor) {
+      // XXX: This has been ported straight from the current debugger
+      // implementation. Since pauseMatchingServiceWorkers expects an origin
+      // to filter matching workers, it only makes sense when we are debugging
+      // a tab. However in theory, parent process debugging could pause all
+      // service workers without matching anything.
+      try {
+        // To support early breakpoint we need to setup the
+        // `pauseMatchingServiceWorkers` mechanism in each process.
+        await targetFront.pauseMatchingServiceWorkers({
+          origin: this.#currentTargetURL.origin,
+        });
+      } catch (e) {
+        if (targetFront.actorID) {
+          throw e;
+        } else {
+          console.warn(
+            "Process target destroyed while calling pauseMatchingServiceWorkers"
+          );
+        }
+      }
+    }
+
+    this._processTargets.add(targetFront);
+    return super._onProcessAvailable({ targetFront });
+  }
+
+  _shouldDestroyTargetsOnNavigation() {
+    return !!this.targetCommand.destroyServiceWorkersOnNavigation;
+  }
+
+  _onProcessDestroyed({ targetFront }) {
+    this._processTargets.delete(targetFront);
+    return super._onProcessDestroyed({ targetFront });
+  }
+
+  _onDocumentEvent(resources) {
+    for (const resource of resources) {
+      if (
+        resource.resourceType !==
+        this.commands.resourceCommand.TYPES.DOCUMENT_EVENT
+      ) {
+        continue;
+      }
+
+      if (resource.name === "will-navigate") {
+        // We rely on will-navigate as the onTargetAvailable for the top-level frame can
+        // happen after the onTargetAvailable for processes (handled in _onProcessAvailable),
+        // where we need the origin we navigate to.
+        this.#currentTargetURL = new URL(resource.newURI);
+        continue;
+      }
+
+      // Note that we rely on "dom-loading" rather than "will-navigate" because the
+      // destroyed/available callbacks should be triggered after the Debugger
+      // has cleaned up its reducers, which happens on "will-navigate".
+      // On the other end, "dom-complete", which is a better mapping of "navigate", is
+      // happening too late (because of resources being throttled), and would cause failures
+      // in test (like browser_target_command_service_workers_navigation.js), as the new worker
+      // target would already be registered at this point, and seen as something that would
+      // need to be destroyed.
+      if (resource.name === "dom-loading") {
+        const allServiceWorkerTargets = this._getAllServiceWorkerTargets();
+        const shouldDestroy = this._shouldDestroyTargetsOnNavigation();
+
+        for (const target of allServiceWorkerTargets) {
+          const isRegisteredBefore =
+            this.targetCommand.isTargetRegistered(target);
+          if (shouldDestroy && isRegisteredBefore) {
+            // Instruct the target command to notify about the worker target destruction
+            // but do not destroy the front as we want to keep using it.
+            // We will notify about it again via onTargetAvailable.
+            this.onTargetDestroyed(target, { shouldDestroyTargetFront: false });
+          }
+
+          // Note: we call isTargetRegistered again because calls to
+          // onTargetDestroyed might have modified the list of registered targets.
+          const isRegisteredAfter =
+            this.targetCommand.isTargetRegistered(target);
+          const isValidTarget = this._supportWorkerTarget(target);
+          if (isValidTarget && !isRegisteredAfter) {
+            // If the target is still valid for the current top target, call
+            // onTargetAvailable as well.
+            this.onTargetAvailable(target);
+          }
+        }
+      }
+    }
+  }
+
+  async _onRegistrationListChanged() {
+    if (this.targetCommand.isDestroyed()) {
+      return;
+    }
+
+    await this._updateRegistrations();
+
+    // Everything after this point is not strictly necessary for sw support
+    // in the target list, but it makes the behavior closer to the previous
+    // listAllWorkers/WorkersListener pair.
+    const allServiceWorkerTargets = this._getAllServiceWorkerTargets();
+    for (const target of allServiceWorkerTargets) {
+      const hasRegistration = this._getRegistrationForWorkerTarget(target);
+      if (!hasRegistration) {
+        // XXX: At this point the worker target is not really destroyed, but
+        // historically, listAllWorkers* APIs stopped returning worker targets
+        // if worker registrations are no longer available.
+        if (this.targetCommand.isTargetRegistered(target)) {
+          // Only emit onTargetDestroyed if it wasn't already done by
+          // onNavigate (ie the target is still tracked by TargetCommand)
+          this.onTargetDestroyed(target);
+        }
+        // Here we only care about service workers which no longer match *any*
+        // registration. The worker will be completely destroyed soon, remove
+        // it from the legacy worker watcher internal targetsByProcess Maps.
+        this._removeTargetReferences(target);
+      }
+    }
+  }
+
+  // Delete the provided worker target from the internal targetsByProcess Maps.
+  _removeTargetReferences(target) {
+    const allProcessTargets = this._getProcessTargets().filter(t =>
+      this.targetsByProcess.get(t)
+    );
+
+    for (const processTarget of allProcessTargets) {
+      this.targetsByProcess.get(processTarget).delete(target);
+    }
+  }
+
+  async _updateRegistrations() {
+    const { registrations } =
+      await this.rootFront.listServiceWorkerRegistrations();
+
+    this._registrations = registrations;
+  }
+
+  _getRegistrationForWorkerTarget(workerTarget) {
+    return this._registrations.find(r => {
+      return (
+        r.evaluatingWorker?.id === workerTarget.id ||
+        r.activeWorker?.id === workerTarget.id ||
+        r.installingWorker?.id === workerTarget.id ||
+        r.waitingWorker?.id === workerTarget.id
+      );
+    });
+  }
+
+  _getProcessTargets() {
+    return [...this._processTargets];
+  }
+
+  // Flatten all service worker targets in all processes.
+  _getAllServiceWorkerTargets() {
+    const allProcessTargets = this._getProcessTargets().filter(target =>
+      this.targetsByProcess.get(target)
+    );
+
+    const serviceWorkerTargets = [];
+    for (const target of allProcessTargets) {
+      serviceWorkerTargets.push(...this.targetsByProcess.get(target));
+    }
+    return serviceWorkerTargets;
+  }
+
+  // Check if the registration is relevant for the current target, ie
+  // corresponds to the same domain.
+  _isRegistrationValidForTarget(registration) {
+    if (this.targetCommand.descriptorFront.isBrowserProcessDescriptor) {
+      // All registrations are valid for main process debugging.
+      return true;
+    }
+
+    if (!this.targetCommand.descriptorFront.isTabDescriptor) {
+      // No support for service worker targets outside of main process &
+      // tab debugging.
+      return false;
+    }
+
+    // For local tabs, we match ServiceWorkerRegistrations and the target
+    // if they share the same hostname for their "url" properties.
+    const targetDomain = this.#currentTargetURL.hostname;
+    try {
+      const registrationDomain = new URL(registration.url).hostname;
+      return registrationDomain === targetDomain;
+    } catch (e) {
+      // XXX: Some registrations have an empty URL.
+      return false;
+    }
+  }
+}
+
+module.exports = LegacyServiceWorkersWatcher;
diff --git a/devtools/shared/commands/target/legacy-target-watchers/legacy-sharedworkers-watcher.js b/devtools/shared/commands/target/legacy-target-watchers/legacy-sharedworkers-watcher.js
new file mode 100644
index 0000000000..b248e6aef7
--- /dev/null
+++ b/devtools/shared/commands/target/legacy-target-watchers/legacy-sharedworkers-watcher.js
@@ -0,0 +1,19 @@
+/* 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/. */
+
+"use strict";
+
+const LegacyWorkersWatcher = require("resource://devtools/shared/commands/target/legacy-target-watchers/legacy-workers-watcher.js");
+
+class LegacySharedWorkersWatcher extends LegacyWorkersWatcher {
+  // Flag used from the parent class to listen to process targets.
+  // Decision tree is complicated, keep all logic in the parent methods.
+  _isSharedWorkerWatcher = true;
+
+  _supportWorkerTarget(workerTarget) {
+    return workerTarget.isSharedWorker;
+  }
+}
+
+module.exports = LegacySharedWorkersWatcher;
diff --git a/devtools/shared/commands/target/legacy-target-watchers/legacy-workers-watcher.js b/devtools/shared/commands/target/legacy-target-watchers/legacy-workers-watcher.js
new file mode 100644
index 0000000000..0baa14757b
--- /dev/null
+++ b/devtools/shared/commands/target/legacy-target-watchers/legacy-workers-watcher.js
@@ -0,0 +1,238 @@
+/* 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/. */
+
+"use strict";
+
+const LegacyProcessesWatcher = require("resource://devtools/shared/commands/target/legacy-target-watchers/legacy-processes-watcher.js");
+
+class LegacyWorkersWatcher {
+  constructor(targetCommand, onTargetAvailable, onTargetDestroyed) {
+    this.targetCommand = targetCommand;
+    this.rootFront = targetCommand.rootFront;
+
+    this.onTargetAvailable = onTargetAvailable;
+    this.onTargetDestroyed = onTargetDestroyed;
+
+    this.targetsByProcess = new WeakMap();
+    this.targetsListeners = new WeakMap();
+
+    this._onProcessAvailable = this._onProcessAvailable.bind(this);
+    this._onProcessDestroyed = this._onProcessDestroyed.bind(this);
+  }
+
+  async _onProcessAvailable({ targetFront }) {
+    this.targetsByProcess.set(targetFront, new Set());
+    // Listen for worker which will be created later
+    const listener = this._workerListChanged.bind(this, targetFront);
+    this.targetsListeners.set(targetFront, listener);
+
+    // If this is the browser toolbox, we have to listen from the RootFront
+    // (see comment in _workerListChanged)
+    const front = targetFront.isParentProcess ? this.rootFront : targetFront;
+    front.on("workerListChanged", listener);
+
+    // We also need to process the already existing workers
+    await this._workerListChanged(targetFront);
+  }
+
+  async _onProcessDestroyed({ targetFront }) {
+    const existingTargets = this.targetsByProcess.get(targetFront);
+
+    // Process the new list to detect the ones being destroyed
+    // Force destroying the targets
+    for (const target of existingTargets) {
+      this.onTargetDestroyed(target);
+
+      target.destroy();
+      existingTargets.delete(target);
+    }
+    this.targetsByProcess.delete(targetFront);
+    this.targetsListeners.delete(targetFront);
+  }
+
+  _supportWorkerTarget(workerTarget) {
+    // subprocess workers are ignored because they take several seconds to
+    // attach to when opening the browser toolbox. See bug 1594597.
+    // When attaching we get the following error:
+    // JavaScript error: resource://devtools/server/startup/worker.js,
+    //   line 37: NetworkError: WorkerDebuggerGlobalScope.loadSubScript: Failed to load worker script at resource://devtools/shared/worker/loader.js (nsresult = 0x805e0006)
+    return (
+      workerTarget.isDedicatedWorker &&
+      !workerTarget.url.startsWith(
+        "resource://gre/modules/subprocess/subprocess_worker"
+      )
+    );
+  }
+
+  async _workerListChanged(targetFront) {
+    // If we're in the Browser Toolbox, query workers from the Root Front instead of the
+    // ParentProcessTarget as the ParentProcess Target filters out the workers to only
+    // show the one from the top level window, whereas we expect the one from all the
+    // windows, and also the window-less ones.
+    // TODO: For Content Toolbox, expose SW of the page, maybe optionally?
+    const front = targetFront.isParentProcess ? this.rootFront : targetFront;
+    if (!front || front.isDestroyed() || this.targetCommand.isDestroyed()) {
+      return;
+    }
+
+    let workers;
+    try {
+      ({ workers } = await front.listWorkers());
+    } catch (e) {
+      // Workers may be added/removed at anytime so that listWorkers request
+      // can be spawn during a toolbox destroy sequence and easily fail
+      if (front.isDestroyed()) {
+        return;
+      }
+      throw e;
+    }
+
+    // Fetch the list of already existing worker targets for this process target front.
+    const existingTargets = this.targetsByProcess.get(targetFront);
+    if (!existingTargets) {
+      // unlisten was called while processing the workerListChanged callback.
+      return;
+    }
+
+    // Process the new list to detect the ones being destroyed
+    // Force destroying the targets
+    for (const target of existingTargets) {
+      if (!workers.includes(target)) {
+        this.onTargetDestroyed(target);
+
+        target.destroy();
+        existingTargets.delete(target);
+      }
+    }
+
+    const promises = workers.map(workerTarget =>
+      this._processNewWorkerTarget(workerTarget, existingTargets)
+    );
+    await Promise.all(promises);
+  }
+
+  // This is overloaded for Service Workers, which records all SW targets,
+  // but only notify about a subset of them.
+  _recordWorkerTarget(workerTarget) {
+    return this._supportWorkerTarget(workerTarget);
+  }
+
+  async _processNewWorkerTarget(workerTarget, existingTargets) {
+    if (
+      !this._recordWorkerTarget(workerTarget) ||
+      existingTargets.has(workerTarget) ||
+      this.targetCommand.isDestroyed()
+    ) {
+      return;
+    }
+
+    // Add the new worker targets to the local list
+    existingTargets.add(workerTarget);
+
+    if (this._supportWorkerTarget(workerTarget)) {
+      await this.onTargetAvailable(workerTarget);
+    }
+  }
+
+  async listen() {
+    // Listen to the current target front.
+    this.target = this.targetCommand.targetFront;
+
+    if (this.target.isParentProcess) {
+      await this.targetCommand.watchTargets({
+        types: [this.targetCommand.TYPES.PROCESS],
+        onAvailable: this._onProcessAvailable,
+        onDestroyed: this._onProcessDestroyed,
+      });
+
+      // The ParentProcessTarget front is considered to be a FRAME instead of a PROCESS.
+      // So process it manually here.
+      await this._onProcessAvailable({ targetFront: this.target });
+      return;
+    }
+
+    if (this._isSharedWorkerWatcher) {
+      // Here we're not in the browser toolbox, and SharedWorker targets are not supported
+      // in regular toolbox (See Bug 1607778)
+      return;
+    }
+
+    if (this._isServiceWorkerWatcher) {
+      this._legacyProcessesWatcher = new LegacyProcessesWatcher(
+        this.targetCommand,
+        async targetFront => {
+          // Service workers only live in content processes.
+          if (!targetFront.isParentProcess) {
+            await this._onProcessAvailable({ targetFront });
+          }
+        },
+        targetFront => {
+          if (!targetFront.isParentProcess) {
+            this._onProcessDestroyed({ targetFront });
+          }
+        }
+      );
+      await this._legacyProcessesWatcher.listen();
+      return;
+    }
+
+    // Here, we're handling Dedicated Workers in content toolbox.
+    this.targetsByProcess.set(
+      this.target,
+      this.targetsByProcess.get(this.target) || new Set()
+    );
+    this._workerListChangedListener = this._workerListChanged.bind(
+      this,
+      this.target
+    );
+    this.target.on("workerListChanged", this._workerListChangedListener);
+    await this._workerListChanged(this.target);
+  }
+
+  _getProcessTargets() {
+    return this.targetCommand.getAllTargets([this.targetCommand.TYPES.PROCESS]);
+  }
+
+  unlisten({ isTargetSwitching } = {}) {
+    // Stop listening for new process targets.
+    if (this.target.isParentProcess) {
+      this.targetCommand.unwatchTargets({
+        types: [this.targetCommand.TYPES.PROCESS],
+        onAvailable: this._onProcessAvailable,
+        onDestroyed: this._onProcessDestroyed,
+      });
+    } else if (this._isServiceWorkerWatcher) {
+      this._legacyProcessesWatcher.unlisten();
+    }
+
+    // Cleanup the targetsByProcess/targetsListeners maps, and unsubscribe from
+    // all targetFronts. Process target fronts are either stored locally when
+    // watching service workers for the content toolbox, or can be retrieved via
+    // the TargetCommand API otherwise (see _getProcessTargets implementations).
+    if (this.target.isParentProcess || this._isServiceWorkerWatcher) {
+      for (const targetFront of this._getProcessTargets()) {
+        const listener = this.targetsListeners.get(targetFront);
+        targetFront.off("workerListChanged", listener);
+
+        // When unlisten is called from a target switch and service workers targets are not
+        // destroyed on navigation, we don't want to remove the targets from targetsByProcess
+        if (
+          !isTargetSwitching ||
+          !this._isServiceWorkerWatcher ||
+          this.targetCommand.destroyServiceWorkersOnNavigation
+        ) {
+          this.targetsByProcess.delete(targetFront);
+        }
+        this.targetsListeners.delete(targetFront);
+      }
+    } else {
+      this.target.off("workerListChanged", this._workerListChangedListener);
+      delete this._workerListChangedListener;
+      this.targetsByProcess.delete(this.target);
+      this.targetsListeners.delete(this.target);
+    }
+  }
+}
+
+module.exports = LegacyWorkersWatcher;
diff --git a/devtools/shared/commands/target/legacy-target-watchers/moz.build b/devtools/shared/commands/target/legacy-target-watchers/moz.build
new file mode 100644
index 0000000000..60fdd7ec22
--- /dev/null
+++ b/devtools/shared/commands/target/legacy-target-watchers/moz.build
@@ -0,0 +1,10 @@
+# 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/.
+
+DevToolsModules(
+    "legacy-processes-watcher.js",
+    "legacy-serviceworkers-watcher.js",
+    "legacy-sharedworkers-watcher.js",
+    "legacy-workers-watcher.js",
+)
diff --git a/devtools/shared/commands/target/moz.build b/devtools/shared/commands/target/moz.build
new file mode 100644
index 0000000000..c23940d7ed
--- /dev/null
+++ b/devtools/shared/commands/target/moz.build
@@ -0,0 +1,17 @@
+# 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/.
+
+DIRS += [
+    "actions",
+    "legacy-target-watchers",
+    "reducers",
+    "selectors",
+]
+
+DevToolsModules(
+    "target-command.js",
+)
+
+if CONFIG["MOZ_BUILD_APP"] != "mobile/android":
+    BROWSER_CHROME_MANIFESTS += ["tests/browser.ini"]
diff --git a/devtools/shared/commands/target/reducers/moz.build b/devtools/shared/commands/target/reducers/moz.build
new file mode 100644
index 0000000000..e9429c1200
--- /dev/null
+++ b/devtools/shared/commands/target/reducers/moz.build
@@ -0,0 +1,7 @@
+# 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/.
+
+DevToolsModules(
+    "targets.js",
+)
diff --git a/devtools/shared/commands/target/reducers/targets.js b/devtools/shared/commands/target/reducers/targets.js
new file mode 100644
index 0000000000..2e93ddd7f0
--- /dev/null
+++ b/devtools/shared/commands/target/reducers/targets.js
@@ -0,0 +1,70 @@
+/* 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/>. */
+"use strict";
+
+const initialReducerState = {
+  // Array of targetFront
+  targets: [],
+  // The selected targetFront instance
+  selected: null,
+  // timestamp of the last time a target was updated (i.e. url/title was updated).
+  // This is used by the EvaluationContextSelector component to re-render the list of
+  // targets when the list itself did not change (no addition/removal)
+  lastTargetRefresh: Date.now(),
+};
+
+function update(state = initialReducerState, action) {
+  switch (action.type) {
+    case "SELECT_TARGET": {
+      const { targetActorID } = action;
+
+      if (state.selected?.actorID === targetActorID) {
+        return state;
+      }
+
+      const selectedTarget = state.targets.find(
+        target => target.actorID === targetActorID
+      );
+
+      // It's possible that the target reducer is missing a target
+      // e.g. workers, remote iframes, etc. (Bug 1594754)
+      if (!selectedTarget) {
+        return state;
+      }
+
+      return { ...state, selected: selectedTarget };
+    }
+
+    case "REGISTER_TARGET": {
+      return {
+        ...state,
+        targets: [...state.targets, action.targetFront],
+      };
+    }
+
+    case "REFRESH_TARGETS": {
+      // The data _in_ targetFront was updated, so we only need to mutate the state,
+      // while keeping the same values.
+      return {
+        ...state,
+        lastTargetRefresh: Date.now(),
+      };
+    }
+
+    case "UNREGISTER_TARGET": {
+      const targets = state.targets.filter(
+        target => target !== action.targetFront
+      );
+
+      let { selected } = state;
+      if (selected === action.targetFront) {
+        selected = null;
+      }
+
+      return { ...state, targets, selected };
+    }
+  }
+  return state;
+}
+module.exports = update;
diff --git a/devtools/shared/commands/target/selectors/moz.build b/devtools/shared/commands/target/selectors/moz.build
new file mode 100644
index 0000000000..e9429c1200
--- /dev/null
+++ b/devtools/shared/commands/target/selectors/moz.build
@@ -0,0 +1,7 @@
+# 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/.
+
+DevToolsModules(
+    "targets.js",
+)
diff --git a/devtools/shared/commands/target/selectors/targets.js b/devtools/shared/commands/target/selectors/targets.js
new file mode 100644
index 0000000000..95da81bbba
--- /dev/null
+++ b/devtools/shared/commands/target/selectors/targets.js
@@ -0,0 +1,20 @@
+/* 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/>. */
+"use strict";
+
+function getToolboxTargets(state) {
+  return state.targets;
+}
+
+function getSelectedTarget(state) {
+  return state.selected;
+}
+
+function getLastTargetRefresh(state) {
+  return state.lastTargetRefresh;
+}
+
+exports.getToolboxTargets = getToolboxTargets;
+exports.getSelectedTarget = getSelectedTarget;
+exports.getLastTargetRefresh = getLastTargetRefresh;
diff --git a/devtools/shared/commands/target/target-command.js b/devtools/shared/commands/target/target-command.js
new file mode 100644
index 0000000000..28e70c9f4b
--- /dev/null
+++ b/devtools/shared/commands/target/target-command.js
@@ -0,0 +1,1173 @@
+/* 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/. */
+
+"use strict";
+
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+
+const BROWSERTOOLBOX_SCOPE_PREF = "devtools.browsertoolbox.scope";
+// Possible values of the previous pref:
+const BROWSERTOOLBOX_SCOPE_EVERYTHING = "everything";
+const BROWSERTOOLBOX_SCOPE_PARENTPROCESS = "parent-process";
+
+// eslint-disable-next-line mozilla/reject-some-requires
+const createStore = require("resource://devtools/client/shared/redux/create-store.js");
+const reducer = require("resource://devtools/shared/commands/target/reducers/targets.js");
+
+loader.lazyRequireGetter(
+  this,
+  ["refreshTargets", "registerTarget", "unregisterTarget"],
+  "resource://devtools/shared/commands/target/actions/targets.js",
+  true
+);
+
+class TargetCommand extends EventEmitter {
+  #selectedTargetFront;
+  /**
+   * This class helps managing, iterating over and listening for Targets.
+   *
+   * It exposes:
+   *  - the top level target, typically the main process target for the browser toolbox
+   *    or the browsing context target for a regular web toolbox
+   *  - target of remoted iframe, in case Fission is enabled and some <iframe>
+   *    are running in a distinct process
+   *  - target switching. If the top level target changes for a new one,
+   *    all the targets are going to be declared as destroyed and the new ones
+   *    will be notified to the user of this API.
+   *
+   * @fires target-tread-wrong-order-on-resume : An event that is emitted when resuming
+   *        the thread throws with the "wrongOrder" error.
+   *
+   * @param {DescriptorFront} descriptorFront
+   *        The context to inspector identified by this descriptor.
+   * @param {WatcherFront} watcherFront
+   *        If available, a reference to the related Watcher Front.
+   * @param {Object} commands
+   *        The commands object with all interfaces defined from devtools/shared/commands/
+   */
+  constructor({ descriptorFront, watcherFront, commands }) {
+    super();
+
+    this.commands = commands;
+    this.descriptorFront = descriptorFront;
+    this.watcherFront = watcherFront;
+    this.rootFront = descriptorFront.client.mainRoot;
+
+    this.store = createStore(reducer);
+    // Name of the store used when calling createProvider.
+    this.storeId = "target-store";
+
+    this._updateBrowserToolboxScope =
+      this._updateBrowserToolboxScope.bind(this);
+
+    Services.prefs.addObserver(
+      BROWSERTOOLBOX_SCOPE_PREF,
+      this._updateBrowserToolboxScope
+    );
+    // Until Watcher actor notify about new top level target when navigating to another process
+    // we have to manually switch to a new target from the client side
+    this.onLocalTabRemotenessChange =
+      this.onLocalTabRemotenessChange.bind(this);
+    if (this.descriptorFront.isTabDescriptor) {
+      this.descriptorFront.on(
+        "remoteness-change",
+        this.onLocalTabRemotenessChange
+      );
+    }
+
+    if (this.isServerTargetSwitchingEnabled()) {
+      // XXX: Will only be used for local tab server side target switching if
+      // the first target is generated from the server.
+      this._onFirstTarget = new Promise(r => (this._resolveOnFirstTarget = r));
+    }
+
+    // Reports if we have at least one listener for the given target type
+    this._listenersStarted = new Set();
+
+    // List of all the target fronts
+    this._targets = new Set();
+    // {Map<Function, Set<targetFront>>} A Map keyed by `onAvailable` function passed to
+    // `watchTargets`, whose initial value is a Set of the existing target fronts at the
+    // time watchTargets is called.
+    this._pendingWatchTargetInitialization = new Map();
+
+    // Listeners for target creation, destruction and selection
+    this._createListeners = new EventEmitter();
+    this._destroyListeners = new EventEmitter();
+    this._selectListeners = new EventEmitter();
+
+    this._onTargetAvailable = this._onTargetAvailable.bind(this);
+    this._onTargetDestroyed = this._onTargetDestroyed.bind(this);
+    this._onTargetSelected = this._onTargetSelected.bind(this);
+    // Bug 1675763: Watcher actor is not available in all situations yet.
+    if (this.watcherFront) {
+      this.watcherFront.on("target-available", this._onTargetAvailable);
+      this.watcherFront.on("target-destroyed", this._onTargetDestroyed);
+    }
+
+    this.legacyImplementation = {};
+
+    // Public flag to allow listening for workers even if the fission pref is off
+    // This allows listening for workers in the content toolbox outside of fission contexts
+    // For now, this is only toggled by tests.
+    this.listenForWorkers =
+      this.rootFront.traits.workerConsoleApiMessagesDispatchedToMainThread ===
+      false;
+    this.listenForServiceWorkers = false;
+    this.destroyServiceWorkersOnNavigation = false;
+
+    // Tells us if we received the first top level target.
+    // If target switching is done on:
+    // * client side, this is done from startListening => _createFirstTarget
+    //                and pull from the Descriptor front.
+    // * server side, this is also done from startListening,
+    //                but we wait for the watcher actor to notify us about it
+    //                via target-available-form avent.
+    this._gotFirstTopLevelTarget = false;
+    this._onResourceAvailable = this._onResourceAvailable.bind(this);
+  }
+
+  get selectedTargetFront() {
+    return this.#selectedTargetFront || this.targetFront;
+  }
+
+  /**
+   * Called fired when BROWSERTOOLBOX_SCOPE_PREF pref changes.
+   * This will enable/disable the full multiprocess debugging.
+   * When enabled we will watch for content process targets and debug all the processes.
+   * When disabled we will only watch for FRAME and WORKER and restrict ourself to parent process resources.
+   */
+  _updateBrowserToolboxScope() {
+    const browserToolboxScope = Services.prefs.getCharPref(
+      BROWSERTOOLBOX_SCOPE_PREF
+    );
+    if (browserToolboxScope == BROWSERTOOLBOX_SCOPE_EVERYTHING) {
+      // Force listening to new additional target types
+      this.startListening();
+    } else if (browserToolboxScope == BROWSERTOOLBOX_SCOPE_PARENTPROCESS) {
+      const disabledTargetTypes = [
+        TargetCommand.TYPES.FRAME,
+        TargetCommand.TYPES.PROCESS,
+      ];
+      // Force unwatching for additional targets types
+      // (we keep listening to workers)
+      // The related targets will be destroyed by the server
+      // and reported as destroyed to the frontend.
+      for (const type of disabledTargetTypes) {
+        this.stopListeningForType(type, {
+          isTargetSwitching: false,
+          isModeSwitching: true,
+        });
+      }
+    }
+  }
+
+  // Called whenever a new Target front is available.
+  // Either because a target was already available as we started calling startListening
+  // or if it has just been created
+  async _onTargetAvailable(targetFront) {
+    // We put the `commands` on the targetFront so it can be retrieved from any front easily.
+    // Without this, protocol.js fronts won't have any easy access to it.
+    // Ideally, Fronts would all be migrated to commands and we would no longer need this hack.
+    targetFront.commands = this.commands;
+
+    // If the new target is a top level target, we are target switching.
+    // Target-switching is only triggered for "local-tab" browsing-context
+    // targets which should always have the topLevelTarget flag initialized
+    // on the server.
+    const isTargetSwitching = targetFront.isTopLevel;
+    const isFirstTarget =
+      targetFront.isTopLevel && !this._gotFirstTopLevelTarget;
+
+    if (this._targets.has(targetFront)) {
+      // The top level target front can be reported via listProcesses in the
+      // case of the BrowserToolbox. For any other target, log an error if it is
+      // already registered.
+      if (targetFront != this.targetFront) {
+        console.error(
+          "Target is already registered in the TargetCommand",
+          targetFront.actorID
+        );
+      }
+      return;
+    }
+
+    if (this.isDestroyed() || targetFront.isDestroyedOrBeingDestroyed()) {
+      return;
+    }
+
+    // Handle top level target switching
+    // Note that, for now, `_onTargetAvailable` isn't called for the *initial* top level target.
+    // i.e. the one that is passed to TargetCommand constructor.
+    if (targetFront.isTopLevel) {
+      // First report that all existing targets are destroyed
+      if (!isFirstTarget) {
+        this._destroyExistingTargetsOnTargetSwitching();
+      }
+
+      // Update the reference to the memoized top level target
+      this.targetFront = targetFront;
+      this.descriptorFront.setTarget(targetFront);
+      this.#selectedTargetFront = null;
+
+      if (isFirstTarget && this.isServerTargetSwitchingEnabled()) {
+        this._gotFirstTopLevelTarget = true;
+        this._resolveOnFirstTarget();
+      }
+    }
+
+    // Map the descriptor typeName to a target type.
+    const targetType = this.getTargetType(targetFront);
+    targetFront.setTargetType(targetType);
+
+    this._targets.add(targetFront);
+    try {
+      await targetFront.attachAndInitThread(this);
+    } catch (e) {
+      console.error("Error when attaching target:", e);
+      this._targets.delete(targetFront);
+      return;
+    }
+
+    for (const targetFrontsSet of this._pendingWatchTargetInitialization.values()) {
+      targetFrontsSet.delete(targetFront);
+    }
+
+    if (this.isDestroyed() || targetFront.isDestroyedOrBeingDestroyed()) {
+      return;
+    }
+
+    this.store.dispatch(registerTarget(targetFront));
+
+    // Then, once the target is attached, notify the target front creation listeners
+    await this._createListeners.emitAsync(targetType, {
+      targetFront,
+      isTargetSwitching,
+    });
+
+    // Re-register the listeners as the top level target changed
+    // and some targets are fetched from it
+    if (targetFront.isTopLevel && !isFirstTarget) {
+      await this.startListening({ isTargetSwitching: true });
+    }
+
+    // These two events are used by tests using the production codepath (i.e. disabling flags.testing)
+    // To be consumed by tests triggering frame navigations, spawning workers...
+    this.emit("processed-available-target", targetFront);
+
+    if (isTargetSwitching) {
+      this.emit("switched-target", targetFront);
+    }
+  }
+
+  _destroyExistingTargetsOnTargetSwitching() {
+    const destroyedTargets = [];
+    for (const target of this._targets) {
+      // We only consider the top level target to be switched
+      const isDestroyedTargetSwitching = target == this.targetFront;
+      const isServiceWorker = target.targetType === this.TYPES.SERVICE_WORKER;
+      const isPopup = target.targetForm.isPopup;
+
+      // Never destroy the popup targets when the top level target is destroyed
+      // as the popup follow a different lifecycle.
+      // Also avoid destroying service worker targets for similar reason,
+      // unless this.destroyServiceWorkersOnNavigation is true.
+      if (
+        !isPopup &&
+        (!isServiceWorker || this.destroyServiceWorkersOnNavigation)
+      ) {
+        this._onTargetDestroyed(target, {
+          isTargetSwitching: isDestroyedTargetSwitching,
+          // Do not destroy service worker front as we may want to keep using it.
+          shouldDestroyTargetFront: !isServiceWorker,
+        });
+        destroyedTargets.push(target);
+      }
+    }
+
+    // Stop listening to legacy listeners as we now have to listen
+    // on the new target.
+    this.stopListening({ isTargetSwitching: true });
+
+    // Remove destroyed target from the cached target list. We don't simply clear the
+    // Map as SW targets might not have been destroyed (i.e. when destroyServiceWorkersOnNavigation
+    // is set to false).
+    for (const target of destroyedTargets) {
+      this._targets.delete(target);
+    }
+  }
+
+  /**
+   * Function fired everytime a target is destroyed.
+   *
+   * This is called either:
+   * - via target-destroyed event fired by the WatcherFront,
+   *   event which is a simple translation of the target-destroyed-form emitted by the WatcherActor.
+   *   Watcher Actor emits this is various condition when the debugged target is meant to be destroyed:
+   *   - the related target context is destroyed (tab closed, worker shut down, content process destroyed, ...),
+   *   - when the DevToolsServerConnection used on the server side to communicate to the client is closed.
+
+   * - by TargetCommand._onTargetAvailable, when a top level target switching happens and all previously
+   *   registered target fronts should be destroyed.
+
+   * - by the legacy Targets listeners, calling this method directly.
+   *   This usecase is meant to be removed someday when all target targets are supported by the Watcher.
+   *   (bug 1687459)
+   *
+   * @param {TargetFront} targetFront
+   *        The target that just got destroyed.
+   * @param {Object} options
+   * @param {Boolean} [options.isTargetSwitching]
+   *        To be set to true when this is about the top level target which is being replaced
+   *        by a new one.
+   *        The passed target should be still the one store in TargetCommand.targetFront
+   *        and will be replaced via a call to onTargetAvailable with a new target front.
+   * @param {Boolean} [options.isModeSwitching]
+   *        To be set to true when the target was destroyed was called as the result of a
+   *        change to the devtools.browsertoolbox.scope pref.
+   * @param {Boolean} [options.shouldDestroyTargetFront]
+   *        By default, the passed target front will be destroyed. But in some cases like
+   *        legacy listeners for service workers we want to keep the front alive.
+   */
+  _onTargetDestroyed(
+    targetFront,
+    {
+      isModeSwitching = false,
+      isTargetSwitching = false,
+      shouldDestroyTargetFront = true,
+    } = {}
+  ) {
+    // The watcher actor may notify us about the destruction of the top level target.
+    // But second argument to this method, isTargetSwitching is only passed from the frontend.
+    // So automatically toggle the isTargetSwitching flag for server side destructions
+    // only if that's about the existing top level target.
+    if (targetFront == this.targetFront) {
+      isTargetSwitching = true;
+    }
+    this._destroyListeners.emit(targetFront.targetType, {
+      targetFront,
+      isTargetSwitching,
+      isModeSwitching,
+    });
+    this._targets.delete(targetFront);
+
+    this.store.dispatch(unregisterTarget(targetFront));
+
+    // If the destroyed target was the selected one, we need to do some cleanup
+    if (this.#selectedTargetFront == targetFront) {
+      // If we're doing a targetSwitch, simply nullify #selectedTargetFront
+      if (isTargetSwitching) {
+        this.#selectedTargetFront = null;
+      } else {
+        // Otherwise we want to select the top level target
+        this.selectTarget(this.targetFront);
+      }
+    }
+
+    if (shouldDestroyTargetFront) {
+      // When calling targetFront.destroy(), we will first call TargetFrontMixin.destroy,
+      // which will try to call `detach` RDP method.
+      // Unfortunately, this request will never complete in some cases like bfcache navigations.
+      // Because of that, the target front will never be completely destroy as it will prevent
+      // calling super.destroy and Front.destroy.
+      // Workaround that by manually calling Front class destroy method:
+      targetFront.baseFrontClassDestroy();
+
+      targetFront.destroy();
+
+      // Delete the attribute we set from _onTargetAvailable so that we avoid leaking commands
+      // if any target front is leaked.
+      delete targetFront.commands;
+    }
+  }
+
+  /**
+   *
+   * @param {TargetFront} targetFront
+   */
+  async _onTargetSelected(targetFront) {
+    if (this.#selectedTargetFront == targetFront) {
+      // Target is already selected, we can bail out.
+      return;
+    }
+
+    this.#selectedTargetFront = targetFront;
+    const targetType = this.getTargetType(targetFront);
+    await this._selectListeners.emitAsync(targetType, {
+      targetFront,
+    });
+  }
+
+  _setListening(type, value) {
+    if (value) {
+      this._listenersStarted.add(type);
+    } else {
+      this._listenersStarted.delete(type);
+    }
+  }
+
+  _isListening(type) {
+    return this._listenersStarted.has(type);
+  }
+
+  /**
+   * Check if the watcher is currently supported.
+   *
+   * When no typeOrTrait is provided, we will only check that the watcher is
+   * available.
+   *
+   * When a typeOrTrait is provided, we will check for an explicit trait on the
+   * watcherFront that indicates either that:
+   *   - a target type is supported
+   *   - or that a custom trait is true
+   *
+   * @param {String} [targetTypeOrTrait]
+   *        Optional target type or trait.
+   * @return {Boolean} true if the watcher is available and supports the
+   *          optional targetTypeOrTrait
+   */
+  hasTargetWatcherSupport(targetTypeOrTrait) {
+    if (targetTypeOrTrait) {
+      // Target types are also exposed as traits, where resource types are
+      // exposed under traits.resources (cf hasResourceWatcherSupport
+      // implementation).
+      return !!this.watcherFront?.traits[targetTypeOrTrait];
+    }
+
+    return !!this.watcherFront;
+  }
+
+  /**
+   * Start listening for targets from the server
+   *
+   * Interact with the actors in order to start listening for new types of targets.
+   * This will fire the _onTargetAvailable function for all already-existing targets,
+   * as well as the next one to be created. It will also call _onTargetDestroyed
+   * everytime a target is reported as destroyed by the actors.
+   * By the time this function resolves, all the already-existing targets will be
+   * reported to _onTargetAvailable.
+   *
+   * @param Object options
+   * @param Boolean options.isTargetSwitching
+   *        Set to true when this is called while a target switching happens. In such case,
+   *        we won't register listener set on the Watcher Actor, but still register listeners
+   *        set via Legacy Listeners.
+   */
+  async startListening({ isTargetSwitching = false } = {}) {
+    // The first time we call this method, we pull the current top level target from the descriptor
+    if (
+      !this.isServerTargetSwitchingEnabled() &&
+      !this._gotFirstTopLevelTarget
+    ) {
+      await this._createFirstTarget();
+    }
+
+    // If no pref are set to true, nor is listenForWorkers set to true,
+    // we won't listen for any additional target. Only the top level target
+    // will be managed. We may still do target-switching.
+    const types = this._computeTargetTypes();
+
+    for (const type of types) {
+      if (this._isListening(type)) {
+        continue;
+      }
+      this._setListening(type, true);
+
+      // Only a few top level targets support the watcher actor at the moment (see WatcherActor
+      // traits in the _form method). Bug 1675763 tracks watcher actor support for all targets.
+      if (this.hasTargetWatcherSupport(type)) {
+        // When we switch to a new top level target, we don't have to stop and restart
+        // Watcher listener as it is independant from the top level target.
+        // This isn't the case for some Legacy Listeners, which fetch targets from the top level target
+        if (!isTargetSwitching) {
+          await this.watcherFront.watchTargets(type);
+        }
+      } else if (LegacyTargetWatchers[type]) {
+        // Instantiate the legacy listener only once for each TargetCommand, and reuse it if we stop and restart listening
+        if (!this.legacyImplementation[type]) {
+          this.legacyImplementation[type] = new LegacyTargetWatchers[type](
+            this,
+            this._onTargetAvailable,
+            this._onTargetDestroyed,
+            this.commands
+          );
+        }
+        await this.legacyImplementation[type].listen();
+      } else {
+        throw new Error(`Unsupported target type '${type}'`);
+      }
+    }
+
+    if (!this._watchingDocumentEvent && !this.isDestroyed()) {
+      // We want to watch DOCUMENT_EVENT in order to update the url and title of target fronts,
+      // as the initial value that is set in them might be erroneous (if the target was
+      // created so early that the document url is still pointing to about:blank and the
+      // html hasn't be parsed yet, so we can't know the <title> content).
+
+      this._watchingDocumentEvent = true;
+      await this.commands.resourceCommand.watchResources(
+        [this.commands.resourceCommand.TYPES.DOCUMENT_EVENT],
+        {
+          onAvailable: this._onResourceAvailable,
+        }
+      );
+    }
+
+    if (this.isServerTargetSwitchingEnabled()) {
+      await this._onFirstTarget;
+    }
+  }
+
+  async _createFirstTarget() {
+    // Note that this is a public attribute, used outside of this class
+    // and helps knowing what is the current top level target we debug.
+    this.targetFront = await this.descriptorFront.getTarget();
+    this.targetFront.setTargetType(this.getTargetType(this.targetFront));
+    this.targetFront.setIsTopLevel(true);
+    this._gotFirstTopLevelTarget = true;
+
+    // See _onTargetAvailable. As this target isn't going through that method
+    // we have to replicate doing that here.
+    this.targetFront.commands = this.commands;
+
+    // Add the top-level target to the list of targets.
+    this._targets.add(this.targetFront);
+    this.store.dispatch(registerTarget(this.targetFront));
+  }
+
+  _computeTargetTypes() {
+    let types = [];
+
+    // We also check for watcher support as some xpcshell tests uses legacy APIs and don't support frames.
+    if (
+      this.descriptorFront.isTabDescriptor &&
+      this.hasTargetWatcherSupport(TargetCommand.TYPES.FRAME)
+    ) {
+      types = [TargetCommand.TYPES.FRAME];
+    } else if (this.descriptorFront.isBrowserProcessDescriptor) {
+      const browserToolboxScope = Services.prefs.getCharPref(
+        BROWSERTOOLBOX_SCOPE_PREF
+      );
+      if (browserToolboxScope == BROWSERTOOLBOX_SCOPE_EVERYTHING) {
+        types = TargetCommand.ALL_TYPES;
+      }
+    }
+    if (this.listenForWorkers && !types.includes(TargetCommand.TYPES.WORKER)) {
+      types.push(TargetCommand.TYPES.WORKER);
+    }
+    if (
+      this.listenForWorkers &&
+      !types.includes(TargetCommand.TYPES.SHARED_WORKER)
+    ) {
+      types.push(TargetCommand.TYPES.SHARED_WORKER);
+    }
+    if (
+      this.listenForServiceWorkers &&
+      !types.includes(TargetCommand.TYPES.SERVICE_WORKER)
+    ) {
+      types.push(TargetCommand.TYPES.SERVICE_WORKER);
+    }
+
+    return types;
+  }
+
+  /**
+   * Stop listening for targets from the server
+   *
+   * @param Object options
+   * @param Boolean options.isTargetSwitching
+   *        Set to true when this is called while a target switching happens. In such case,
+   *        we won't unregister listener set on the Watcher Actor, but still unregister
+   *        listeners set via Legacy Listeners.
+   */
+  stopListening({ isTargetSwitching = false } = {}) {
+    // As DOCUMENT_EVENT isn't using legacy listener,
+    // there is no need to stop and restart it in case of target switching.
+    if (this._watchingDocumentEvent && !isTargetSwitching) {
+      this.commands.resourceCommand.unwatchResources(
+        [this.commands.resourceCommand.TYPES.DOCUMENT_EVENT],
+        {
+          onAvailable: this._onResourceAvailable,
+        }
+      );
+      this._watchingDocumentEvent = false;
+    }
+
+    for (const type of TargetCommand.ALL_TYPES) {
+      this.stopListeningForType(type, { isTargetSwitching });
+    }
+  }
+
+  /**
+   * Stop listening for targets of a given type from the server
+   *
+   * @param String type
+   *        target type we want to stop listening for
+   * @param Object options
+   * @param Boolean options.isTargetSwitching
+   *        Set to true when this is called while a target switching happens. In such case,
+   *        we won't unregister listener set on the Watcher Actor, but still unregister
+   *        listeners set via Legacy Listeners.
+   * @param Boolean options.isModeSwitching
+   *        Set to true when this is called as the result of a change to the
+   *        devtools.browsertoolbox.scope pref.
+   */
+  stopListeningForType(type, { isTargetSwitching, isModeSwitching }) {
+    if (!this._isListening(type)) {
+      return;
+    }
+    this._setListening(type, false);
+
+    // Only a few top level targets support the watcher actor at the moment (see WatcherActor
+    // traits in the _form method). Bug 1675763 tracks watcher actor support for all targets.
+    if (this.hasTargetWatcherSupport(type)) {
+      // When we switch to a new top level target, we don't have to stop and restart
+      // Watcher listener as it is independant from the top level target.
+      // This isn't the case for some Legacy Listeners, which fetch targets from the top level target
+      // Also, TargetCommand.destroy may be called after the client is closed.
+      // So avoid calling the RDP method in that situation.
+      if (!isTargetSwitching && !this.watcherFront.isDestroyed()) {
+        this.watcherFront.unwatchTargets(type, { isModeSwitching });
+      }
+    } else if (this.legacyImplementation[type]) {
+      this.legacyImplementation[type].unlisten({
+        isTargetSwitching,
+        isModeSwitching,
+      });
+    } else {
+      throw new Error(`Unsupported target type '${type}'`);
+    }
+  }
+
+  getTargetType(target) {
+    const { typeName } = target;
+    if (typeName == "windowGlobalTarget") {
+      return TargetCommand.TYPES.FRAME;
+    }
+
+    if (
+      typeName == "contentProcessTarget" ||
+      typeName == "parentProcessTarget"
+    ) {
+      return TargetCommand.TYPES.PROCESS;
+    }
+
+    if (typeName == "workerDescriptor" || typeName == "workerTarget") {
+      if (target.isSharedWorker) {
+        return TargetCommand.TYPES.SHARED_WORKER;
+      }
+
+      if (target.isServiceWorker) {
+        return TargetCommand.TYPES.SERVICE_WORKER;
+      }
+
+      return TargetCommand.TYPES.WORKER;
+    }
+
+    throw new Error("Unsupported target typeName: " + typeName);
+  }
+
+  _matchTargetType(type, target) {
+    return type === target.targetType;
+  }
+
+  _onResourceAvailable(resources) {
+    for (const resource of resources) {
+      if (
+        resource.resourceType ===
+        this.commands.resourceCommand.TYPES.DOCUMENT_EVENT
+      ) {
+        const { targetFront } = resource;
+        if (resource.title !== undefined && targetFront?.setTitle) {
+          targetFront.setTitle(resource.title);
+        }
+        if (resource.url !== undefined && targetFront?.setUrl) {
+          targetFront.setUrl(resource.url);
+        }
+        if (
+          !resource.isFrameSwitching &&
+          // `url` is set on the targetFront when we receive dom-loading, and `title` when
+          // `dom-interactive` is received. Here we're only updating the window title in
+          // the "newer" event.
+          resource.name === "dom-interactive"
+        ) {
+          // We just updated the targetFront title and url, force a refresh
+          // so that the EvaluationContext selector update them.
+          this.store.dispatch(refreshTargets());
+        }
+      }
+    }
+  }
+
+  /**
+   * Listen for the creation and/or destruction of target fronts matching one of the provided types.
+   *
+   * @param {Object} options
+   * @param {Array<String>} options.types
+   *        The type of target to listen for. Constant of TargetCommand.TYPES.
+   * @param {Function} options.onAvailable
+   *        Mandatory callback fired when a target has been just created or was already available.
+   *        The function is called with a single object argument containing the following properties:
+   *        - {TargetFront} targetFront: The target Front
+   *        - {Boolean} isTargetSwitching: Is this target relates to a navigation and
+   *                    this replaced a previously available target, this flag will be true
+   * @param {Function} options.onDestroyed
+   *        Optional callback fired in case of target front destruction.
+   *        The function is called with the same arguments than onAvailable.
+   * @param {Function} options.onSelected
+   *        Optional callback fired when a given target is selected from the iframe picker
+   *        The function is called with a single object argument containing the following properties:
+   *        - {TargetFront} targetFront: The target Front
+   */
+  async watchTargets(options = {}) {
+    const availableOptions = [
+      "types",
+      "onAvailable",
+      "onDestroyed",
+      "onSelected",
+    ];
+    const unsupportedKeys = Object.keys(options).filter(
+      key => !availableOptions.includes(key)
+    );
+    if (unsupportedKeys.length) {
+      throw new Error(
+        `TargetCommand.watchTargets does not expect the following options: ${unsupportedKeys.join(
+          ", "
+        )}`
+      );
+    }
+
+    const { types, onAvailable, onDestroyed, onSelected } = options;
+    if (typeof onAvailable != "function") {
+      throw new Error(
+        "TargetCommand.watchTargets expects a function for the onAvailable option"
+      );
+    }
+
+    for (const type of types) {
+      if (!this._isValidTargetType(type)) {
+        throw new Error(
+          `TargetCommand.watchTargets invoked with an unknown type: "${type}"`
+        );
+      }
+    }
+
+    // Notify about already existing target of these types
+    const targetFronts = [...this._targets].filter(targetFront =>
+      types.includes(targetFront.targetType)
+    );
+    this._pendingWatchTargetInitialization.set(
+      onAvailable,
+      new Set(targetFronts)
+    );
+    const promises = targetFronts.map(async targetFront => {
+      // Attach the targets that aren't attached yet (e.g. the initial top-level target),
+      // and wait for the other ones to be fully attached.
+      try {
+        await targetFront.attachAndInitThread(this);
+      } catch (e) {
+        console.error("Error when attaching target:", e);
+        return;
+      }
+
+      // It can happen that onAvailable was already called with this targetFront at
+      // this time (via _onTargetAvailable). If that's the case, we don't want to call
+      // onAvailable a second time.
+      if (
+        this._pendingWatchTargetInitialization &&
+        this._pendingWatchTargetInitialization.has(onAvailable) &&
+        !this._pendingWatchTargetInitialization
+          .get(onAvailable)
+          .has(targetFront)
+      ) {
+        return;
+      }
+
+      try {
+        // Ensure waiting for eventual async create listeners
+        // which may setup things regarding the existing targets
+        // and listen callsite may care about the full initialization
+        await onAvailable({
+          targetFront,
+          isTargetSwitching: false,
+        });
+      } catch (e) {
+        // Prevent throwing when onAvailable handler throws on one target
+        // so that it can try to register the other targets
+        console.error(
+          "Exception when calling onAvailable handler",
+          e.message,
+          e
+        );
+      }
+    });
+
+    for (const type of types) {
+      this._createListeners.on(type, onAvailable);
+      if (onDestroyed) {
+        this._destroyListeners.on(type, onDestroyed);
+      }
+      if (onSelected) {
+        this._selectListeners.on(type, onSelected);
+      }
+    }
+
+    await Promise.all(promises);
+    this._pendingWatchTargetInitialization.delete(onAvailable);
+  }
+
+  /**
+   * Stop listening for the creation and/or destruction of a given type of target fronts.
+   * See `watchTargets()` for documentation of the arguments.
+   */
+  unwatchTargets(options = {}) {
+    const availableOptions = [
+      "types",
+      "onAvailable",
+      "onDestroyed",
+      "onSelected",
+    ];
+    const unsupportedKeys = Object.keys(options).filter(
+      key => !availableOptions.includes(key)
+    );
+    if (unsupportedKeys.length) {
+      throw new Error(
+        `TargetCommand.unwatchTargets does not expect the following options: ${unsupportedKeys.join(
+          ", "
+        )}`
+      );
+    }
+
+    const { types, onAvailable, onDestroyed, onSelected } = options;
+    if (typeof onAvailable != "function") {
+      throw new Error(
+        "TargetCommand.unwatchTargets expects a function for the onAvailable option"
+      );
+    }
+
+    for (const type of types) {
+      if (!this._isValidTargetType(type)) {
+        throw new Error(
+          `TargetCommand.unwatchTargets invoked with an unknown type: "${type}"`
+        );
+      }
+
+      this._createListeners.off(type, onAvailable);
+      if (onDestroyed) {
+        this._destroyListeners.off(type, onDestroyed);
+      }
+      if (onSelected) {
+        this._selectListeners.off(type, onSelected);
+      }
+    }
+    this._pendingWatchTargetInitialization.delete(onAvailable);
+  }
+
+  /**
+   * Retrieve all the current target fronts of a given type.
+   *
+   * @param {Array<String>} types
+   *        The types of target to retrieve. Array of TargetCommand.TYPES
+   * @return {Array<TargetFront>} Array of target fronts matching any of the
+   *         provided types.
+   */
+  getAllTargets(types) {
+    if (!types?.length) {
+      throw new Error("getAllTargets expects a non-empty array of types");
+    }
+
+    const targets = [...this._targets].filter(target =>
+      types.some(type => this._matchTargetType(type, target))
+    );
+
+    return targets;
+  }
+
+  /**
+   * Retrieve all the target fronts in the selected target tree (including the selected
+   * target itself).
+   *
+   * @param {Array<String>} types
+   *        The types of target to retrieve. Array of TargetCommand.TYPES
+   * @return {Promise<Array<TargetFront>>} Promise that resolves to an array of target fronts.
+   */
+  async getAllTargetsInSelectedTargetTree(types) {
+    const allTargets = this.getAllTargets(types);
+    if (this.isTopLevelTargetSelected()) {
+      return allTargets;
+    }
+
+    const targets = [this.selectedTargetFront];
+    for (const target of allTargets) {
+      const isInSelectedTree = await target.isTargetAnAncestor(
+        this.selectedTargetFront
+      );
+
+      if (isInSelectedTree) {
+        targets.push(target);
+      }
+    }
+    return targets;
+  }
+
+  /**
+   * For all the target fronts of given types, retrieve all the target-scoped fronts of the given types.
+   *
+   * @param {Array<String>} targetTypes
+   *        The types of target to iterate over. Constant of TargetCommand.TYPES.
+   * @param {String} frontType
+   *        The type of target-scoped front to retrieve. It can be "inspector", "console", "thread",...
+   * @param {Object} options
+   * @param {Boolean} options.onlyInSelectedTargetTree
+   *        Set to true to only get the fronts for targets who are in the "targets tree"
+   *        of the selected target.
+   */
+  async getAllFronts(
+    targetTypes,
+    frontType,
+    { onlyInSelectedTargetTree = false } = {}
+  ) {
+    if (!Array.isArray(targetTypes) || !targetTypes?.length) {
+      throw new Error("getAllFronts expects a non-empty array of target types");
+    }
+    const promises = [];
+    const targets = !onlyInSelectedTargetTree
+      ? this.getAllTargets(targetTypes)
+      : await this.getAllTargetsInSelectedTargetTree(targetTypes);
+    for (const target of targets) {
+      // For still-attaching worker targets, the thread or console front may not yet be available,
+      // whereas TargetMixin.getFront will throw if the actorID isn't available in targetForm.
+      // Also ignore destroyed targets. For some reason the previous methods fetching targets
+      // can sometime return destroyed targets.
+      if (
+        (frontType == "thread" && !target.targetForm.threadActor) ||
+        (frontType == "console" && !target.targetForm.consoleActor) ||
+        target.isDestroyed()
+      ) {
+        continue;
+      }
+
+      promises.push(target.getFront(frontType));
+    }
+    return Promise.all(promises);
+  }
+
+  /**
+   * This function is triggered by an event sent by the TabDescriptor when
+   * the tab navigates to a distinct process.
+   *
+   * @param TargetFront targetFront
+   *        The WindowGlobalTargetFront instance that navigated to another process
+   */
+  async onLocalTabRemotenessChange(targetFront) {
+    if (this.isServerTargetSwitchingEnabled()) {
+      // For server-side target switching, everything will be handled by the
+      // _onTargetAvailable callback.
+      return;
+    }
+
+    // TabDescriptor may emit the event with a null targetFront, interpret that as if the previous target
+    // has already been destroyed
+    if (targetFront) {
+      // Wait for the target to be destroyed so that LocalTabCommandsFactory clears its memoized target for this tab
+      await targetFront.once("target-destroyed");
+    }
+
+    // Fetch the new target from the descriptor.
+    const newTarget = await this.descriptorFront.getTarget();
+
+    // If a navigation happens while we try to get the target for the page that triggered
+    // the remoteness change, `getTarget` will return null. In such case, we'll get the
+    // "next" target through onTargetAvailable so it's safe to bail here.
+    if (!newTarget) {
+      console.warn(
+        `Couldn't get the target for descriptor ${this.descriptorFront.actorID}`
+      );
+      return;
+    }
+
+    this.switchToTarget(newTarget);
+  }
+
+  /**
+   * Reload the current top level target.
+   * This only works for targets inheriting from WindowGlobalTarget.
+   *
+   * @param {Boolean} bypassCache
+   *        If true, the reload will be forced to bypass any cache.
+   */
+  async reloadTopLevelTarget(bypassCache = false) {
+    if (!this.descriptorFront.traits.supportsReloadDescriptor) {
+      throw new Error("The top level target doesn't support being reloaded");
+    }
+
+    // Wait for the next DOCUMENT_EVENT's dom-complete event
+    // Wait for waitForNextResource completion before reloading, otherwise we might miss the dom-complete event.
+    // This can happen if `ResourceCommand.watchResources` made by `waitForNextResource` is still pending
+    // while the reload already started and finished loading the document early.
+    const { onResource: onReloaded } =
+      await this.commands.resourceCommand.waitForNextResource(
+        this.commands.resourceCommand.TYPES.DOCUMENT_EVENT,
+        {
+          ignoreExistingResources: true,
+          predicate(resource) {
+            return resource.name == "dom-complete";
+          },
+        }
+      );
+
+    await this.descriptorFront.reloadDescriptor({ bypassCache });
+
+    await onReloaded;
+  }
+
+  /**
+   * Called when the top level target is replaced by a new one.
+   * Typically when we navigate to another domain which requires to be loaded in a distinct process.
+   *
+   * @param {TargetFront} newTarget
+   *        The new top level target to debug.
+   */
+  async switchToTarget(newTarget) {
+    // Notify about this new target to creation listeners
+    // _onTargetAvailable will also destroy all previous target before notifying about this new one.
+    await this._onTargetAvailable(newTarget);
+  }
+
+  /**
+   * Called when the user selects a frame in the iframe picker.
+   *
+   * @param {WindowGlobalTargetFront} targetFront
+   *        The target front we want the toolbox to focus on.
+   */
+  selectTarget(targetFront) {
+    return this._onTargetSelected(targetFront);
+  }
+
+  /**
+   * Returns true if the top-level frame is the selected one
+   *
+   * @returns {Boolean}
+   */
+  isTopLevelTargetSelected() {
+    return this.selectedTargetFront === this.targetFront;
+  }
+
+  /**
+   * Returns true if a non top-level frame is the selected one in the iframe picker.
+   *
+   * @returns {Boolean}
+   */
+  isNonTopLevelTargetSelected() {
+    return this.selectedTargetFront !== this.targetFront;
+  }
+
+  isTargetRegistered(targetFront) {
+    return this._targets.has(targetFront);
+  }
+
+  getParentTarget(targetFront) {
+    // Note that there are edgecases:
+    // * Until bug 1741927 is fixed and we remove non-EFT codepath entirely,
+    //   we may receive a `parentInnerWindowId` that doesn't relate to any target.
+    //   This happens when the parent document of the targetFront is a document loaded in the
+    //   same process as its parent document. In such scenario, and only when EFT is disabled,
+    //   we won't instantiate a target for the parent document of the targetFront.
+    // * `parentInnerWindowId` could be null in some case like for tabs in the MBT
+    //   we should report the top level target as parent. That's what `getParentWindowGlobalTarget` does.
+    //   Once we can stop using getParentWindowGlobalTarget for the other edgecase we will be able to
+    //   replace it with such fallback: `return this.targetFront;`.
+    //   browser_target_command_frames.js will help you get things right.
+    const { parentInnerWindowId } = targetFront.targetForm;
+    if (parentInnerWindowId) {
+      const targets = this.getAllTargets([TargetCommand.TYPES.FRAME]);
+      const parent = targets.find(
+        target => target.innerWindowId == parentInnerWindowId
+      );
+      // Until EFT is the only codepath supported (bug 1741927), we will fallback to `getParentWindowGlobalTarget`
+      // as we may not have a target if the parent is an iframe running in the same process as its parent.
+      if (parent) {
+        return parent;
+      }
+    }
+
+    // Note that all callsites which care about FRAME additional target
+    // should all have a toolbox using the watcher actor.
+    // It should be: MBT, regular tab toolbox and web extension.
+    // The others which still don't support watcher don't spawn FRAME targets:
+    // browser content toolbox and service workers.
+
+    return this.watcherFront.getParentWindowGlobalTarget(
+      targetFront.browsingContextID
+    );
+  }
+
+  isDestroyed() {
+    return this._isDestroyed;
+  }
+
+  isServerTargetSwitchingEnabled() {
+    if (this.descriptorFront.isServerTargetSwitchingEnabled) {
+      return this.descriptorFront.isServerTargetSwitchingEnabled();
+    }
+    return false;
+  }
+
+  _isValidTargetType(type) {
+    return this.ALL_TYPES.includes(type);
+  }
+
+  destroy() {
+    this.stopListening();
+    this._createListeners.off();
+    this._destroyListeners.off();
+    this._selectListeners.off();
+
+    this.#selectedTargetFront = null;
+    this._isDestroyed = true;
+
+    Services.prefs.removeObserver(
+      BROWSERTOOLBOX_SCOPE_PREF,
+      this._updateBrowserToolboxScope
+    );
+  }
+}
+
+/**
+ * All types of target:
+ */
+TargetCommand.TYPES = TargetCommand.prototype.TYPES = {
+  PROCESS: "process",
+  FRAME: "frame",
+  WORKER: "worker",
+  SHARED_WORKER: "shared_worker",
+  SERVICE_WORKER: "service_worker",
+};
+TargetCommand.ALL_TYPES = TargetCommand.prototype.ALL_TYPES = Object.values(
+  TargetCommand.TYPES
+);
+
+const LegacyTargetWatchers = {};
+loader.lazyRequireGetter(
+  LegacyTargetWatchers,
+  TargetCommand.TYPES.PROCESS,
+  "resource://devtools/shared/commands/target/legacy-target-watchers/legacy-processes-watcher.js"
+);
+loader.lazyRequireGetter(
+  LegacyTargetWatchers,
+  TargetCommand.TYPES.WORKER,
+  "resource://devtools/shared/commands/target/legacy-target-watchers/legacy-workers-watcher.js"
+);
+loader.lazyRequireGetter(
+  LegacyTargetWatchers,
+  TargetCommand.TYPES.SHARED_WORKER,
+  "resource://devtools/shared/commands/target/legacy-target-watchers/legacy-sharedworkers-watcher.js"
+);
+loader.lazyRequireGetter(
+  LegacyTargetWatchers,
+  TargetCommand.TYPES.SERVICE_WORKER,
+  "resource://devtools/shared/commands/target/legacy-target-watchers/legacy-serviceworkers-watcher.js"
+);
+
+module.exports = TargetCommand;
diff --git a/devtools/shared/commands/target/tests/browser.ini b/devtools/shared/commands/target/tests/browser.ini
new file mode 100644
index 0000000000..b28e700de0
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser.ini
@@ -0,0 +1,48 @@
+[DEFAULT]
+tags = devtools
+subsuite = devtools
+support-files =
+  !/devtools/client/shared/test/shared-head.js
+  !/devtools/client/shared/test/telemetry-test-helpers.js
+  !/devtools/client/shared/test/highlighter-test-actor.js
+  head.js
+  simple_document.html
+  incremental-js-value-script.sjs
+  fission_document.html
+  fission_iframe.html
+  test_service_worker.js
+  test_sw_page.html
+  test_sw_page_worker.js
+  test_worker.js
+
+[browser_target_command_bfcache.js]
+[browser_target_command_browser_workers.js]
+[browser_target_command_detach.js]
+[browser_target_command_frames_popups.js]
+skip-if =
+  win10_2004 && debug && fission && socketprocess_networking # high frequency intermittent
+[browser_target_command_frames_reload_server_side_targets.js]
+skip-if = !fission
+[browser_target_command_frames.js]
+[browser_target_command_getAllTargets.js]
+[browser_target_command_invalid_api_usage.js]
+[browser_target_command_scope_flag.js]
+[browser_target_command_processes.js]
+[browser_target_command_reload.js]
+[browser_target_command_service_workers.js]
+skip-if =
+  http3  # Bug 1781324
+[browser_target_command_service_workers_navigation.js]
+skip-if =
+  os == "linux" && bits == 64 # Bug 1726270
+  os == "win" && bits == 64 # Bug 1726270
+  os == "mac" && fission # Bug 1726270
+[browser_target_command_switchToTarget.js]
+[browser_target_command_tab_workers.js]
+[browser_target_command_tab_workers_bfcache_navigation.js]
+skip-if = debug # Bug 1721859
+[browser_target_command_various_descriptors.js]
+skip-if =
+  os == "linux" && bits == 64 && !debug #Bug 1701056
+[browser_target_command_watchTargets.js]
+[browser_watcher_actor_getter_caching.js]
diff --git a/devtools/shared/commands/target/tests/browser_target_command_bfcache.js b/devtools/shared/commands/target/tests/browser_target_command_bfcache.js
new file mode 100644
index 0000000000..a5deeb9260
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_bfcache.js
@@ -0,0 +1,499 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API when bfcache navigations happen
+
+const TEST_COM_URL = URL_ROOT_SSL + "simple_document.html";
+
+add_task(async function () {
+  // Disable the preloaded process as it gets created lazily and may interfere
+  // with process count assertions
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+  // This preference helps destroying the content process when we close the tab
+  await pushPref("dom.ipc.keepProcessesAlive.web", 1);
+
+  info("## Test with bfcache in parent DISABLED");
+  await pushPref("fission.bfcacheInParent", false);
+  await testTopLevelNavigations(false);
+  await testIframeNavigations(false);
+  await testTopLevelNavigationsOnDocumentWithIframe(false);
+
+  // bfcacheInParent only works if sessionHistoryInParent is enable
+  // so only test it if both settings are enabled.
+  // (it looks like sessionHistoryInParent is enabled by default when fission is enabled)
+  if (Services.appinfo.sessionHistoryInParent) {
+    info("## Test with bfcache in parent ENABLED");
+    await pushPref("fission.bfcacheInParent", true);
+    await testTopLevelNavigations(true);
+    await testIframeNavigations(true);
+    await testTopLevelNavigationsOnDocumentWithIframe(true);
+  }
+});
+
+async function testTopLevelNavigations(bfcacheInParent) {
+  info(" # Test TOP LEVEL navigations");
+  // Create a TargetCommand for a given test tab
+  const tab = await addTab(TEST_COM_URL);
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Assert that watchTargets will call the create callback for all existing frames
+  const targets = [];
+  const onAvailable = async ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    ok(targetFront.isTopLevel, "all targets of this test are top level");
+    targets.push(targetFront);
+  };
+  const destroyedTargets = [];
+  const onDestroyed = async ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    ok(targetFront.isTopLevel, "all targets of this test are top level");
+    destroyedTargets.push(targetFront);
+  };
+
+  await targetCommand.watchTargets({
+    types: [TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+  is(targets.length, 1, "retrieved only the top level target");
+  is(targets[0], targetCommand.targetFront, "the target is the top level one");
+  is(
+    destroyedTargets.length,
+    0,
+    "We get no destruction when calling watchTargets"
+  );
+  ok(
+    targets[0].targetForm.followWindowGlobalLifeCycle,
+    "the first server side target follows the WindowGlobal lifecycle, when server target switching is enabled"
+  );
+
+  // Navigate to the same page with query params
+  info("Load the second page");
+  const secondPageUrl = TEST_COM_URL + "?second-load";
+  const previousBrowsingContextID = gBrowser.selectedBrowser.browsingContext.id;
+  ok(
+    previousBrowsingContextID,
+    "Fetch the tab's browsing context id before navigation"
+  );
+  const onLoaded = BrowserTestUtils.browserLoaded(
+    gBrowser.selectedBrowser,
+    false,
+    secondPageUrl
+  );
+  BrowserTestUtils.loadURIString(gBrowser.selectedBrowser, secondPageUrl);
+  await onLoaded;
+
+  // Assert BrowsingContext changes as it impact the behavior of targets
+  if (bfcacheInParent) {
+    isnot(
+      previousBrowsingContextID,
+      gBrowser.selectedBrowser.browsingContext.id,
+      "When bfcacheInParent is enabled, same-origin navigations spawn new BrowsingContext"
+    );
+  } else {
+    is(
+      previousBrowsingContextID,
+      gBrowser.selectedBrowser.browsingContext.id,
+      "When bfcacheInParent is disabled, same-origin navigations re-use the same BrowsingContext"
+    );
+  }
+
+  // Same-origin navigations also spawn a new top level target
+  await waitFor(
+    () => targets.length == 2,
+    "wait for the next top level target"
+  );
+  is(
+    targets[1],
+    targetCommand.targetFront,
+    "the second target is the top level one"
+  );
+  // As targetFront.url isn't reliable and might be about:blank,
+  // try to assert that we got the right target via other means.
+  // outerWindowID should change when navigating to another process,
+  // while it would stay equal for in-process navigations.
+  is(
+    targets[1].outerWindowID,
+    gBrowser.selectedBrowser.outerWindowID,
+    "the second target is for the second page"
+  );
+  ok(
+    targets[1].targetForm.followWindowGlobalLifeCycle,
+    "the new server side target follows the WindowGlobal lifecycle"
+  );
+  ok(targets[0].isDestroyed(), "the first target is destroyed");
+  is(destroyedTargets.length, 1, "We get one target being destroyed...");
+  is(destroyedTargets[0], targets[0], "...and that's the first one");
+
+  // Go back to the first page, this should be a bfcache navigation, and,
+  // we should get a new target
+  info("Go back to the first page");
+  gBrowser.selectedBrowser.goBack();
+
+  await waitFor(
+    () => targets.length == 3,
+    "wait for the next top level target"
+  );
+  is(
+    targets[2],
+    targetCommand.targetFront,
+    "the third target is the top level one"
+  );
+  // Here as this is revived from cache, the url should always be correct
+  is(targets[2].url, TEST_COM_URL, "the third target is for the first url");
+  ok(
+    targets[2].targetForm.followWindowGlobalLifeCycle,
+    "the third target for bfcache navigations is following the WindowGlobal lifecycle"
+  );
+  ok(targets[1].isDestroyed(), "the second target is destroyed");
+  is(
+    destroyedTargets.length,
+    2,
+    "We get one additional target being destroyed..."
+  );
+  is(destroyedTargets[1], targets[1], "...and that's the second one");
+
+  // Wait for full attach in order to having breaking any pending requests
+  // when navigating to another page and switching to new process and target.
+  await waitForAllTargetsToBeAttached(targetCommand);
+
+  // Go forward and resurect the second page, this should also be a bfcache navigation, and,
+  // get a new target.
+  info("Go forward to the second page");
+
+  // When a new target will be created, we need to wait until it's fully processed
+  // to avoid pending promises.
+  const onNewTargetProcessed = bfcacheInParent
+    ? new Promise(resolve => {
+        targetCommand.on(
+          "processed-available-target",
+          function onProcessedAvailableTarget(targetFront) {
+            if (targetFront === targets[3]) {
+              resolve();
+              targetCommand.off(
+                "processed-available-target",
+                onProcessedAvailableTarget
+              );
+            }
+          }
+        );
+      })
+    : null;
+
+  gBrowser.selectedBrowser.goForward();
+
+  await waitFor(
+    () => targets.length == 4,
+    "wait for the next top level target"
+  );
+  is(
+    targets[3],
+    targetCommand.targetFront,
+    "the 4th target is the top level one"
+  );
+  // Same here, as the document is revived from the cache, the url should always be correct
+  is(targets[3].url, secondPageUrl, "the 4th target is for the second url");
+  ok(
+    targets[3].targetForm.followWindowGlobalLifeCycle,
+    "the 4th target for bfcache navigations is following the WindowGlobal lifecycle"
+  );
+  ok(targets[2].isDestroyed(), "the third target is destroyed");
+  is(
+    destroyedTargets.length,
+    3,
+    "We get one additional target being destroyed..."
+  );
+  is(destroyedTargets[2], targets[2], "...and that's the third one");
+
+  // Wait for full attach in order to having breaking any pending requests
+  // when navigating to another page and switching to new process and target.
+  await waitForAllTargetsToBeAttached(targetCommand);
+  await onNewTargetProcessed;
+
+  await waitForAllTargetsToBeAttached(targetCommand);
+
+  targetCommand.unwatchTargets({ types: [TYPES.FRAME], onAvailable });
+
+  BrowserTestUtils.removeTab(tab);
+
+  await commands.destroy();
+}
+
+async function testTopLevelNavigationsOnDocumentWithIframe(bfcacheInParent) {
+  info(" # Test TOP LEVEL navigations on document with iframe");
+  // Create a TargetCommand for a given test tab
+  const tab =
+    await addTab(`https://example.com/document-builder.sjs?id=top&html=
+    <h1>Top level</h1>
+    <iframe src="${encodeURIComponent(
+      "https://example.com/document-builder.sjs?id=iframe&html=<h2>In iframe</h2>"
+    )}">
+    </iframe>`);
+  const getLocationIdParam = url =>
+    new URLSearchParams(new URL(url).search).get("id");
+
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Assert that watchTargets will call the create callback for all existing frames
+  const targets = [];
+  const onAvailable = async ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    targets.push(targetFront);
+  };
+  const destroyedTargets = [];
+  const onDestroyed = async ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    destroyedTargets.push(targetFront);
+  };
+
+  await targetCommand.watchTargets({
+    types: [TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+
+  if (isEveryFrameTargetEnabled()) {
+    is(
+      targets.length,
+      2,
+      "retrieved targets for top level and iframe documents"
+    );
+    is(
+      targets[0],
+      targetCommand.targetFront,
+      "the target is the top level one"
+    );
+    is(
+      getLocationIdParam(targets[1].url),
+      "iframe",
+      "the second target is the iframe one"
+    );
+  } else {
+    is(targets.length, 1, "retrieved only the top level target");
+    is(
+      targets[0],
+      targetCommand.targetFront,
+      "the target is the top level one"
+    );
+  }
+
+  is(
+    destroyedTargets.length,
+    0,
+    "We get no destruction when calling watchTargets"
+  );
+
+  info("Navigate to a new page");
+  let targetCountBeforeNavigation = targets.length;
+  const secondPageUrl = `https://example.com/document-builder.sjs?html=second`;
+  const onLoaded = BrowserTestUtils.browserLoaded(
+    gBrowser.selectedBrowser,
+    false,
+    secondPageUrl
+  );
+  BrowserTestUtils.loadURIString(gBrowser.selectedBrowser, secondPageUrl);
+  await onLoaded;
+
+  // Same-origin navigations also spawn a new top level target
+  await waitFor(
+    () => targets.length == targetCountBeforeNavigation + 1,
+    "wait for the next top level target"
+  );
+  is(
+    targets.at(-1),
+    targetCommand.targetFront,
+    "the new target is the top level one"
+  );
+
+  ok(targets[0].isDestroyed(), "the first target is destroyed");
+  if (isEveryFrameTargetEnabled()) {
+    ok(targets[1].isDestroyed(), "the second target is destroyed");
+    is(destroyedTargets.length, 2, "The two targets were destroyed");
+  } else {
+    is(destroyedTargets.length, 1, "Only one target was destroyed");
+  }
+
+  // Go back to the first page, this should be a bfcache navigation, and,
+  // we should get a new target (or 2 if EFT is enabled)
+  targetCountBeforeNavigation = targets.length;
+  info("Go back to the first page");
+  gBrowser.selectedBrowser.goBack();
+
+  await waitFor(
+    () =>
+      targets.length ===
+      targetCountBeforeNavigation + (isEveryFrameTargetEnabled() ? 2 : 1),
+    "wait for the next top level target"
+  );
+
+  if (isEveryFrameTargetEnabled()) {
+    await waitFor(() => targets.at(-2).url && targets.at(-1).url);
+    is(
+      getLocationIdParam(targets.at(-2).url),
+      "top",
+      "the first new target is for the top document…"
+    );
+    is(
+      getLocationIdParam(targets.at(-1).url),
+      "iframe",
+      "…and the second one is for the iframe"
+    );
+  } else {
+    is(
+      getLocationIdParam(targets.at(-1).url),
+      "top",
+      "the new target is for the first url"
+    );
+  }
+
+  ok(
+    targets[targetCountBeforeNavigation - 1].isDestroyed(),
+    "the target for the second page is destroyed"
+  );
+  is(
+    destroyedTargets.length,
+    targetCountBeforeNavigation,
+    "We get one additional target being destroyed…"
+  );
+  is(
+    destroyedTargets.at(-1),
+    targets[targetCountBeforeNavigation - 1],
+    "…and that's the second page one"
+  );
+
+  await waitForAllTargetsToBeAttached(targetCommand);
+
+  targetCommand.unwatchTargets({
+    types: [TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+
+  BrowserTestUtils.removeTab(tab);
+
+  await commands.destroy();
+}
+
+async function testIframeNavigations() {
+  info(" # Test IFRAME navigations");
+  // Create a TargetCommand for a given test tab
+  const tab = await addTab(
+    `http://example.org/document-builder.sjs?html=<iframe src="${TEST_COM_URL}"></iframe>`
+  );
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Assert that watchTargets will call the create callback for all existing frames
+  const targets = [];
+  const onAvailable = async ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    targets.push(targetFront);
+  };
+  await targetCommand.watchTargets({ types: [TYPES.FRAME], onAvailable });
+
+  // When fission/EFT is off, there isn't much to test for iframes as they are debugged
+  // when the unique top level target
+  if (!isFissionEnabled() && !isEveryFrameTargetEnabled()) {
+    is(
+      targets.length,
+      1,
+      "Without fission/EFT, there is only the top level target"
+    );
+    await commands.destroy();
+    return;
+  }
+  is(targets.length, 2, "retrieved the top level and the iframe targets");
+  is(
+    targets[0],
+    targetCommand.targetFront,
+    "the first target is the top level one"
+  );
+  is(targets[1].url, TEST_COM_URL, "the second target is the iframe one");
+
+  // Navigate to the same page with query params
+  info("Load the second page");
+  const secondPageUrl = TEST_COM_URL + "?second-load";
+  await SpecialPowers.spawn(
+    gBrowser.selectedBrowser,
+    [secondPageUrl],
+    function (url) {
+      const iframe = content.document.querySelector("iframe");
+      iframe.src = url;
+    }
+  );
+
+  await waitFor(() => targets.length == 3, "wait for the next target");
+  is(targets[2].url, secondPageUrl, "the second target is for the second url");
+  ok(targets[1].isDestroyed(), "the first target is destroyed");
+
+  // Go back to the first page, this should be a bfcache navigation, and,
+  // we should get a new target
+  info("Go back to the first page");
+  const iframeBrowsingContext = await SpecialPowers.spawn(
+    gBrowser.selectedBrowser,
+    [],
+    function () {
+      const iframe = content.document.querySelector("iframe");
+      return iframe.browsingContext;
+    }
+  );
+  await SpecialPowers.spawn(iframeBrowsingContext, [], function () {
+    content.history.back();
+  });
+
+  await waitFor(() => targets.length == 4, "wait for the next target");
+  is(targets[3].url, TEST_COM_URL, "the third target is for the first url");
+  ok(targets[2].isDestroyed(), "the second target is destroyed");
+
+  // Go forward and resurect the second page, this should also be a bfcache navigation, and,
+  // get a new target.
+  info("Go forward to the second page");
+  await SpecialPowers.spawn(iframeBrowsingContext, [], function () {
+    content.history.forward();
+  });
+
+  await waitFor(() => targets.length == 5, "wait for the next target");
+  is(targets[4].url, secondPageUrl, "the 4th target is for the second url");
+  ok(targets[3].isDestroyed(), "the third target is destroyed");
+
+  targetCommand.unwatchTargets({ types: [TYPES.FRAME], onAvailable });
+
+  await waitForAllTargetsToBeAttached(targetCommand);
+
+  BrowserTestUtils.removeTab(tab);
+
+  await commands.destroy();
+}
diff --git a/devtools/shared/commands/target/tests/browser_target_command_browser_workers.js b/devtools/shared/commands/target/tests/browser_target_command_browser_workers.js
new file mode 100644
index 0000000000..181cfa2614
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_browser_workers.js
@@ -0,0 +1,246 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API around workers
+
+const FISSION_TEST_URL = URL_ROOT_SSL + "fission_document.html";
+const WORKER_FILE = "test_worker.js";
+const CHROME_WORKER_URL = CHROME_URL_ROOT + WORKER_FILE;
+const SERVICE_WORKER_URL = URL_ROOT_SSL + "test_service_worker.js";
+
+add_task(async function () {
+  // Enabled fission's pref as the TargetCommand is almost disabled without it
+  await pushPref("devtools.browsertoolbox.scope", "everything");
+
+  // Disable the preloaded process as it creates processes intermittently
+  // which forces the emission of RDP requests we aren't correctly waiting for.
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+
+  const tab = await addTab(FISSION_TEST_URL);
+
+  info("Test TargetCommand against workers via the parent process target");
+
+  // Instantiate a worker in the parent process
+  // eslint-disable-next-line no-unused-vars
+  const worker = new Worker(CHROME_WORKER_URL + "#simple-worker");
+  // eslint-disable-next-line no-unused-vars
+  const sharedWorker = new SharedWorker(CHROME_WORKER_URL + "#shared-worker");
+
+  const commands = await CommandsFactory.forMainProcess();
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+  await targetCommand.startListening();
+
+  // Very naive sanity check against getAllTargets([workerType])
+  info("Check that getAllTargets returned the expected targets");
+  const workers = await targetCommand.getAllTargets([TYPES.WORKER]);
+  const hasWorker = workers.find(workerTarget => {
+    return workerTarget.url == CHROME_WORKER_URL + "#simple-worker";
+  });
+  ok(hasWorker, "retrieve the target for the worker");
+
+  const sharedWorkers = await targetCommand.getAllTargets([
+    TYPES.SHARED_WORKER,
+  ]);
+  const hasSharedWorker = sharedWorkers.find(workerTarget => {
+    return workerTarget.url == CHROME_WORKER_URL + "#shared-worker";
+  });
+  ok(hasSharedWorker, "retrieve the target for the shared worker");
+
+  const serviceWorkers = await targetCommand.getAllTargets([
+    TYPES.SERVICE_WORKER,
+  ]);
+  const hasServiceWorker = serviceWorkers.find(workerTarget => {
+    return workerTarget.url == SERVICE_WORKER_URL;
+  });
+  ok(hasServiceWorker, "retrieve the target for the service worker");
+
+  info(
+    "Check that calling getAllTargets again return the same target instances"
+  );
+  const workers2 = await targetCommand.getAllTargets([TYPES.WORKER]);
+  const sharedWorkers2 = await targetCommand.getAllTargets([
+    TYPES.SHARED_WORKER,
+  ]);
+  const serviceWorkers2 = await targetCommand.getAllTargets([
+    TYPES.SERVICE_WORKER,
+  ]);
+  is(workers2.length, workers.length, "retrieved the same number of workers");
+  is(
+    sharedWorkers2.length,
+    sharedWorkers.length,
+    "retrieved the same number of shared workers"
+  );
+  is(
+    serviceWorkers2.length,
+    serviceWorkers.length,
+    "retrieved the same number of service workers"
+  );
+
+  workers.sort(sortFronts);
+  workers2.sort(sortFronts);
+  sharedWorkers.sort(sortFronts);
+  sharedWorkers2.sort(sortFronts);
+  serviceWorkers.sort(sortFronts);
+  serviceWorkers2.sort(sortFronts);
+
+  for (let i = 0; i < workers.length; i++) {
+    is(workers[i], workers2[i], `worker ${i} targets are the same`);
+  }
+  for (let i = 0; i < sharedWorkers2.length; i++) {
+    is(
+      sharedWorkers[i],
+      sharedWorkers2[i],
+      `shared worker ${i} targets are the same`
+    );
+  }
+  for (let i = 0; i < serviceWorkers2.length; i++) {
+    is(
+      serviceWorkers[i],
+      serviceWorkers2[i],
+      `service worker ${i} targets are the same`
+    );
+  }
+
+  info(
+    "Check that watchTargets will call the create callback for all existing workers"
+  );
+  const targets = [];
+  const topLevelTarget = await commands.targetCommand.targetFront;
+  const onAvailable = async ({ targetFront }) => {
+    ok(
+      targetFront.targetType === TYPES.WORKER ||
+        targetFront.targetType === TYPES.SHARED_WORKER ||
+        targetFront.targetType === TYPES.SERVICE_WORKER,
+      "We are only notified about worker targets"
+    );
+    ok(
+      targetFront == topLevelTarget
+        ? targetFront.isTopLevel
+        : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
+    );
+    targets.push(targetFront);
+  };
+  await targetCommand.watchTargets({
+    types: [TYPES.WORKER, TYPES.SHARED_WORKER, TYPES.SERVICE_WORKER],
+    onAvailable,
+  });
+  is(
+    targets.length,
+    workers.length + sharedWorkers.length + serviceWorkers.length,
+    "retrieved the same number of workers via watchTargets"
+  );
+
+  targets.sort(sortFronts);
+  const allWorkers = workers
+    .concat(sharedWorkers, serviceWorkers)
+    .sort(sortFronts);
+
+  for (let i = 0; i < allWorkers.length; i++) {
+    is(
+      allWorkers[i],
+      targets[i],
+      `worker ${i} targets are the same via watchTargets`
+    );
+  }
+
+  targetCommand.unwatchTargets({
+    types: [TYPES.WORKER, TYPES.SHARED_WORKER, TYPES.SERVICE_WORKER],
+    onAvailable,
+  });
+
+  // Create a new worker and see if the worker target is reported
+  const onWorkerCreated = new Promise(resolve => {
+    const onAvailable2 = async ({ targetFront }) => {
+      if (targets.includes(targetFront)) {
+        return;
+      }
+      targetCommand.unwatchTargets({
+        types: [TYPES.WORKER],
+        onAvailable: onAvailable2,
+      });
+      resolve(targetFront);
+    };
+    targetCommand.watchTargets({
+      types: [TYPES.WORKER],
+      onAvailable: onAvailable2,
+    });
+  });
+  // eslint-disable-next-line no-unused-vars
+  const worker2 = new Worker(CHROME_WORKER_URL + "#second");
+  info("Wait for the second worker to be created");
+  const workerTarget = await onWorkerCreated;
+
+  is(
+    workerTarget.url,
+    CHROME_WORKER_URL + "#second",
+    "This worker target is about the new worker"
+  );
+  is(
+    workerTarget.name,
+    "test_worker.js#second",
+    "The worker target has the expected name"
+  );
+
+  const workers3 = await targetCommand.getAllTargets([TYPES.WORKER]);
+  const hasWorker2 = workers3.find(
+    ({ url }) => url == `${CHROME_WORKER_URL}#second`
+  );
+  ok(hasWorker2, "retrieve the target for tab via getAllTargets");
+
+  info(
+    "Check that terminating the worker does trigger the onDestroyed callback"
+  );
+  const onWorkerDestroyed = new Promise(resolve => {
+    const emptyFn = () => {};
+    const onDestroyed = ({ targetFront }) => {
+      targetCommand.unwatchTargets({
+        types: [TYPES.WORKER],
+        onAvailable: emptyFn,
+        onDestroyed,
+      });
+      resolve(targetFront);
+    };
+
+    targetCommand.watchTargets({
+      types: [TYPES.WORKER],
+      onAvailable: emptyFn,
+      onDestroyed,
+    });
+  });
+  worker2.terminate();
+  const workerTargetFront = await onWorkerDestroyed;
+  ok(true, "onDestroyed was called when the worker was terminated");
+
+  workerTargetFront.isTopLevel;
+  ok(
+    true,
+    "isTopLevel can be called on the target front after onDestroyed was called"
+  );
+
+  workerTargetFront.name;
+  ok(
+    true,
+    "name can be accessed on the target front after onDestroyed was called"
+  );
+
+  targetCommand.destroy();
+
+  info("Unregister service workers so they don't appear in other tests.");
+  await unregisterAllServiceWorkers(commands.client);
+
+  await commands.destroy();
+
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    // registrationPromise is set by the test page.
+    const registration = await content.wrappedJSObject.registrationPromise;
+    registration.unregister();
+  });
+});
+
+function sortFronts(f1, f2) {
+  return f1.actorID < f2.actorID;
+}
diff --git a/devtools/shared/commands/target/tests/browser_target_command_detach.js b/devtools/shared/commands/target/tests/browser_target_command_detach.js
new file mode 100644
index 0000000000..a0056cd7a5
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_detach.js
@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand's when detaching the top target
+//
+// Do this with the "remote tab" codepath, which will avoid
+// destroying the DevToolsClient when the target is destroyed.
+// Otherwise, with "local tab", the client is closed and everything is destroy
+// on both client and server side.
+
+const TEST_URL = "data:text/html,test-page";
+
+add_task(async function () {
+  info(" ### Test detaching the top target");
+
+  // Create a TargetCommand for a given test tab
+  const tab = await addTab(TEST_URL);
+
+  info("Create a first commands, which will destroy its top target");
+  const commands = await CommandsFactory.forRemoteTab(
+    tab.linkedBrowser.browserId
+  );
+  const targetCommand = commands.targetCommand;
+
+  // We have to start listening in order to ensure having a targetFront available
+  await targetCommand.startListening();
+
+  info("Call any target front method, to ensure it works fine");
+  await targetCommand.targetFront.focus();
+
+  // Destroying the target front should end up calling "WindowGlobalTargetActor.detach"
+  // which should destroy the target on the server side
+  await targetCommand.targetFront.destroy();
+
+  info(
+    "Now create a second commands after destroy, to see if we can spawn a new, functional target"
+  );
+  const secondCommands = await CommandsFactory.forRemoteTab(
+    tab.linkedBrowser.browserId,
+    {
+      client: commands.client,
+    }
+  );
+  const secondTargetCommand = secondCommands.targetCommand;
+
+  // We have to start listening in order to ensure having a targetFront available
+  await secondTargetCommand.startListening();
+
+  info("Call any target front method, to ensure it works fine");
+  await secondTargetCommand.targetFront.focus();
+
+  BrowserTestUtils.removeTab(tab);
+
+  info("Close the two commands");
+  await commands.destroy();
+  await secondCommands.destroy();
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_frames.js b/devtools/shared/commands/target/tests/browser_target_command_frames.js
new file mode 100644
index 0000000000..bfa297801a
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_frames.js
@@ -0,0 +1,649 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API around frames
+
+const FISSION_TEST_URL = URL_ROOT_SSL + "fission_document.html";
+const IFRAME_URL = URL_ROOT_ORG_SSL + "fission_iframe.html";
+const SECOND_PAGE_URL = "https://example.org/document-builder.sjs?html=org";
+
+const PID_REGEXP = /^\d+$/;
+
+add_task(async function () {
+  // Disable bfcache for Fission for now.
+  // If Fission is disabled, the pref is no-op.
+  await SpecialPowers.pushPrefEnv({
+    set: [["fission.bfcacheInParent", false]],
+  });
+
+  // Enabled fission prefs
+  await pushPref("devtools.browsertoolbox.scope", "everything");
+  // Disable the preloaded process as it gets created lazily and may interfere
+  // with process count assertions
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+  // This preference helps destroying the content process when we close the tab
+  await pushPref("dom.ipc.keepProcessesAlive.web", 1);
+
+  // Test fetching the frames from the main process descriptor
+  await testBrowserFrames();
+
+  // Test fetching the frames from a tab descriptor
+  await testTabFrames();
+
+  // Test what happens with documents running in the parent process
+  await testOpeningOnParentProcessDocument();
+  await testNavigationToParentProcessDocument();
+
+  // Test what happens with about:blank documents
+  await testOpeningOnAboutBlankDocument();
+  await testNavigationToAboutBlankDocument();
+
+  await testNestedIframes();
+});
+
+async function testOpeningOnParentProcessDocument() {
+  info("Test opening against a parent process document");
+  const tab = await addTab("about:robots");
+  is(
+    tab.linkedBrowser.browsingContext.currentWindowGlobal.osPid,
+    -1,
+    "The tab is loaded in the parent process"
+  );
+
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const frames = await targetCommand.getAllTargets([targetCommand.TYPES.FRAME]);
+  is(frames.length, 1);
+  is(frames[0].url, "about:robots", "target url is correct");
+  is(
+    frames[0],
+    targetCommand.targetFront,
+    "the target is the current top level one"
+  );
+
+  await commands.destroy();
+}
+
+async function testNavigationToParentProcessDocument() {
+  info("Test navigating to parent process document");
+  const firstLocation = "data:text/html,foo";
+  const secondLocation = "about:robots";
+
+  const tab = await addTab(firstLocation);
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  // When the first top level target is created from the server,
+  // `startListening` emits a spurious switched-target event
+  // which isn't necessarily emited before it resolves.
+  // So ensure waiting for it, otherwise we may resolve too eagerly
+  // in our expected listener.
+  const onSwitchedTarget1 = targetCommand.once("switched-target");
+  await targetCommand.startListening();
+  info("wait for first top level target");
+  await onSwitchedTarget1;
+
+  const firstTarget = targetCommand.targetFront;
+  is(firstTarget.url, firstLocation, "first target url is correct");
+
+  info("Navigate to a parent process page");
+  const onSwitchedTarget = targetCommand.once("switched-target");
+  const browser = tab.linkedBrowser;
+  const onLoaded = BrowserTestUtils.browserLoaded(browser);
+  await BrowserTestUtils.loadURIString(browser, secondLocation);
+  await onLoaded;
+  is(
+    browser.browsingContext.currentWindowGlobal.osPid,
+    -1,
+    "The tab is loaded in the parent process"
+  );
+
+  await onSwitchedTarget;
+  isnot(targetCommand.targetFront, firstTarget, "got a new target");
+
+  // Check that calling getAllTargets([frame]) return the same target instances
+  const frames = await targetCommand.getAllTargets([targetCommand.TYPES.FRAME]);
+  is(frames.length, 1);
+  is(frames[0].url, secondLocation, "second target url is correct");
+  is(
+    frames[0],
+    targetCommand.targetFront,
+    "second target is the current top level one"
+  );
+
+  await commands.destroy();
+}
+
+async function testOpeningOnAboutBlankDocument() {
+  info("Test opening against about:blank document");
+  const tab = await addTab("about:blank");
+
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const frames = await targetCommand.getAllTargets([targetCommand.TYPES.FRAME]);
+  is(frames.length, 1);
+  is(frames[0].url, "about:blank", "target url is correct");
+  is(
+    frames[0],
+    targetCommand.targetFront,
+    "the target is the current top level one"
+  );
+
+  await commands.destroy();
+}
+
+async function testNavigationToAboutBlankDocument() {
+  info("Test navigating to about:blank");
+  const firstLocation = "data:text/html,foo";
+  const secondLocation = "about:blank";
+
+  const tab = await addTab(firstLocation);
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  // When the first top level target is created from the server,
+  // `startListening` emits a spurious switched-target event
+  // which isn't necessarily emited before it resolves.
+  // So ensure waiting for it, otherwise we may resolve too eagerly
+  // in our expected listener.
+  const onSwitchedTarget1 = targetCommand.once("switched-target");
+  await targetCommand.startListening();
+  info("wait for first top level target");
+  await onSwitchedTarget1;
+
+  const firstTarget = targetCommand.targetFront;
+  is(firstTarget.url, firstLocation, "first target url is correct");
+
+  info("Navigate to about:blank page");
+  const onSwitchedTarget = targetCommand.once("switched-target");
+  const browser = tab.linkedBrowser;
+  const onLoaded = BrowserTestUtils.browserLoaded(browser);
+  await BrowserTestUtils.loadURIString(browser, secondLocation);
+  await onLoaded;
+
+  await onSwitchedTarget;
+  isnot(targetCommand.targetFront, firstTarget, "got a new target");
+
+  // Check that calling getAllTargets([frame]) return the same target instances
+  const frames = await targetCommand.getAllTargets([targetCommand.TYPES.FRAME]);
+  is(frames.length, 1);
+  is(frames[0].url, secondLocation, "second target url is correct");
+  is(
+    frames[0],
+    targetCommand.targetFront,
+    "second target is the current top level one"
+  );
+
+  await commands.destroy();
+}
+
+async function testBrowserFrames() {
+  info("Test TargetCommand against frames via the parent process target");
+
+  const aboutBlankTab = await addTab("about:blank");
+
+  const commands = await CommandsFactory.forMainProcess();
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+  await targetCommand.startListening();
+
+  // Very naive sanity check against getAllTargets([frame])
+  const frames = await targetCommand.getAllTargets([TYPES.FRAME]);
+  const hasBrowserDocument = frames.find(
+    frameTarget => frameTarget.url == window.location.href
+  );
+  ok(hasBrowserDocument, "retrieve the target for the browser document");
+
+  const hasAboutBlankDocument = frames.find(
+    frameTarget =>
+      frameTarget.browsingContextID ==
+      aboutBlankTab.linkedBrowser.browsingContext.id
+  );
+  ok(hasAboutBlankDocument, "retrieve the target for the about:blank tab");
+
+  // Check that calling getAllTargets([frame]) return the same target instances
+  const frames2 = await targetCommand.getAllTargets([TYPES.FRAME]);
+  is(frames2.length, frames.length, "retrieved the same number of frames");
+
+  function sortFronts(f1, f2) {
+    return f1.actorID < f2.actorID;
+  }
+  frames.sort(sortFronts);
+  frames2.sort(sortFronts);
+  for (let i = 0; i < frames.length; i++) {
+    is(frames[i], frames2[i], `frame ${i} targets are the same`);
+  }
+
+  // Assert that watchTargets will call the create callback for all existing frames
+  const targets = [];
+  const topLevelTarget = targetCommand.targetFront;
+
+  const noParentTarget = await topLevelTarget.getParentTarget();
+  is(noParentTarget, null, "The top level target has no parent target");
+
+  const onAvailable = ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    ok(
+      targetFront == topLevelTarget
+        ? targetFront.isTopLevel
+        : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
+    );
+    ok(
+      PID_REGEXP.test(targetFront.processID),
+      `Target has processID of expected shape (${targetFront.processID})`
+    );
+    targets.push(targetFront);
+  };
+  await targetCommand.watchTargets({ types: [TYPES.FRAME], onAvailable });
+  is(
+    targets.length,
+    frames.length,
+    "retrieved the same number of frames via watchTargets"
+  );
+
+  frames.sort(sortFronts);
+  targets.sort(sortFronts);
+  for (let i = 0; i < frames.length; i++) {
+    is(
+      frames[i],
+      targets[i],
+      `frame ${i} targets are the same via watchTargets`
+    );
+  }
+
+  async function addTabAndAssertNewTarget(url) {
+    const previousTargetCount = targets.length;
+    const tab = await addTab(url);
+    await waitFor(
+      () => targets.length == previousTargetCount + 1,
+      "Wait for all expected targets after tab opening"
+    );
+    is(
+      targets.length,
+      previousTargetCount + 1,
+      "Opening a tab reported a new frame"
+    );
+    const newTabTarget = targets.at(-1);
+    is(newTabTarget.url, url, "This frame target is about the new tab");
+    // Internaly, the tab, which uses a <browser type='content'> element is considered detached from their owner document
+    // and so the target is having a null parentInnerWindowId. But the framework will attach all non-top-level targets
+    // as children of the top level.
+    const tabParentTarget = await newTabTarget.getParentTarget();
+    is(
+      tabParentTarget,
+      targetCommand.targetFront,
+      "tab's WindowGlobal/BrowsingContext is detached and has no parent, but we report them as children of the top level target"
+    );
+
+    const frames3 = await targetCommand.getAllTargets([TYPES.FRAME]);
+    const hasTabDocument = frames3.find(target => target.url == url);
+    ok(hasTabDocument, "retrieve the target for tab via getAllTargets");
+
+    return tab;
+  }
+
+  info("Open a tab loaded in content process");
+  await addTabAndAssertNewTarget("data:text/html,content-process-page");
+
+  info("Open a tab loaded in the parent process");
+  const parentProcessTab = await addTabAndAssertNewTarget("about:robots");
+  is(
+    parentProcessTab.linkedBrowser.browsingContext.currentWindowGlobal.osPid,
+    -1,
+    "The tab is loaded in the parent process"
+  );
+
+  info("Open a new content window via window.open");
+  info("First open a tab on .org domain");
+  const tabUrl = "https://example.org/document-builder.sjs?html=org";
+  await addTabAndAssertNewTarget(tabUrl);
+  const previousTargetCount = targets.length;
+
+  info("Then open a popup on .com domain");
+  const popupUrl = "https://example.com/document-builder.sjs?html=com";
+  const onPopupOpened = BrowserTestUtils.waitForNewTab(gBrowser, popupUrl);
+  await SpecialPowers.spawn(gBrowser.selectedBrowser, [popupUrl], async url => {
+    content.window.open(url, "_blank");
+  });
+  await onPopupOpened;
+
+  await waitFor(
+    () => targets.length == previousTargetCount + 1,
+    "Wait for all expected targets after window.open()"
+  );
+  is(
+    targets.length,
+    previousTargetCount + 1,
+    "Opening a new content window reported a new frame"
+  );
+  is(
+    targets.at(-1).url,
+    popupUrl,
+    "This frame target is about the new content window"
+  );
+
+  // About:blank are a bit special because we ignore a transcient about:blank
+  // document when navigating to another process. But we should not ignore
+  // tabs, loading a real, final about:blank document.
+  info("Open a tab with about:blank");
+  await addTabAndAssertNewTarget("about:blank");
+
+  // Until we start spawning target for all WindowGlobals,
+  // including the one running in the same process as their parent,
+  // we won't create dedicated target for new top level windows.
+  // Instead, these document will be debugged via the ParentProcessTargetActor.
+  info("Open a top level chrome window");
+  const expectedTargets = targets.length;
+  const chromeWindow = Services.ww.openWindow(
+    null,
+    "about:robots",
+    "_blank",
+    "chrome",
+    null
+  );
+  await wait(250);
+  is(
+    targets.length,
+    expectedTargets,
+    "New top level window shouldn't spawn new target"
+  );
+  chromeWindow.close();
+
+  targetCommand.unwatchTargets({ types: [TYPES.FRAME], onAvailable });
+
+  targetCommand.destroy();
+  await waitForAllTargetsToBeAttached(targetCommand);
+
+  await commands.destroy();
+}
+
+async function testTabFrames(mainRoot) {
+  info("Test TargetCommand against frames via a tab target");
+
+  // Create a TargetCommand for a given test tab
+  const tab = await addTab(FISSION_TEST_URL);
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Check that calling getAllTargets([frame]) return the same target instances
+  const frames = await targetCommand.getAllTargets([TYPES.FRAME]);
+  // When fission is enabled, we also get the remote example.org iframe.
+  const expectedFramesCount =
+    isFissionEnabled() || isEveryFrameTargetEnabled() ? 2 : 1;
+  is(
+    frames.length,
+    expectedFramesCount,
+    "retrieved the expected number of targets"
+  );
+
+  // Assert that watchTargets will call the create callback for all existing frames
+  const targets = [];
+  const destroyedTargets = [];
+  const topLevelTarget = targetCommand.targetFront;
+  const onAvailable = ({ targetFront, isTargetSwitching }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    ok(
+      PID_REGEXP.test(targetFront.processID),
+      `Target has processID of expected shape (${targetFront.processID})`
+    );
+    targets.push({ targetFront, isTargetSwitching });
+  };
+  const onDestroyed = ({ targetFront, isTargetSwitching }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    ok(
+      targetFront == topLevelTarget
+        ? targetFront.isTopLevel
+        : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
+    );
+    destroyedTargets.push({ targetFront, isTargetSwitching });
+  };
+  await targetCommand.watchTargets({
+    types: [TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+  is(
+    targets.length,
+    frames.length,
+    "retrieved the same number of frames via watchTargets"
+  );
+  is(destroyedTargets.length, 0, "Should be no destroyed target initialy");
+
+  for (const frame of frames) {
+    ok(
+      targets.find(({ targetFront }) => targetFront === frame),
+      "frame " + frame.actorID + " target is the same via watchTargets"
+    );
+  }
+  is(
+    targets[0].targetFront.url,
+    FISSION_TEST_URL,
+    "First target should be the top document one"
+  );
+  is(
+    targets[0].targetFront.isTopLevel,
+    true,
+    "First target is a top level one"
+  );
+  is(
+    !targets[0].isTargetSwitching,
+    true,
+    "First target is not considered as a target switching"
+  );
+  const noParentTarget = await targets[0].targetFront.getParentTarget();
+  is(noParentTarget, null, "The top level target has no parent target");
+
+  if (isFissionEnabled() || isEveryFrameTargetEnabled()) {
+    is(
+      targets[1].targetFront.url,
+      IFRAME_URL,
+      "Second target should be the iframe one"
+    );
+    is(
+      !targets[1].targetFront.isTopLevel,
+      true,
+      "Iframe target isn't top level"
+    );
+    is(
+      !targets[1].isTargetSwitching,
+      true,
+      "Iframe target isn't a target swich"
+    );
+    const parentTarget = await targets[1].targetFront.getParentTarget();
+    is(
+      parentTarget,
+      targets[0].targetFront,
+      "The parent target for the iframe is the top level target"
+    );
+  }
+
+  // Before navigating to another process, ensure cleaning up everything from the first page
+  await waitForAllTargetsToBeAttached(targetCommand);
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    // registrationPromise is set by the test page.
+    const registration = await content.wrappedJSObject.registrationPromise;
+    registration.unregister();
+  });
+
+  info("Navigate to another domain and process (if fission is enabled)");
+  // When a new target will be created, we need to wait until it's fully processed
+  // to avoid pending promises.
+  const onNewTargetProcessed = targetCommand.once("processed-available-target");
+
+  const browser = tab.linkedBrowser;
+  const onLoaded = BrowserTestUtils.browserLoaded(browser);
+  await BrowserTestUtils.loadURIString(browser, SECOND_PAGE_URL);
+  await onLoaded;
+
+  if (isFissionEnabled() || isEveryFrameTargetEnabled()) {
+    const afterNavigationFramesCount = 3;
+    await waitFor(
+      () => targets.length == afterNavigationFramesCount,
+      "Wait for all expected targets after navigation"
+    );
+    is(
+      targets.length,
+      afterNavigationFramesCount,
+      "retrieved all targets after navigation"
+    );
+    // As targetFront.url isn't reliable and might be about:blank,
+    // try to assert that we got the right target via other means.
+    // outerWindowID should change when navigating to another process,
+    // while it would stay equal for in-process navigations.
+    is(
+      targets[2].targetFront.outerWindowID,
+      browser.outerWindowID,
+      "The new target should be the newly loaded document"
+    );
+    is(
+      targets[2].isTargetSwitching,
+      true,
+      "and should be flagged as a target switching"
+    );
+
+    is(
+      destroyedTargets.length,
+      2,
+      "The two existing targets should be destroyed"
+    );
+    is(
+      destroyedTargets[0].targetFront,
+      targets[1].targetFront,
+      "The first destroyed should be the iframe one"
+    );
+    is(
+      destroyedTargets[0].isTargetSwitching,
+      false,
+      "the target destruction is not flagged as target switching for iframes"
+    );
+    is(
+      destroyedTargets[1].targetFront,
+      targets[0].targetFront,
+      "The second destroyed should be the previous top level one (because it is delayed to be fired *after* will-navigate)"
+    );
+    is(
+      destroyedTargets[1].isTargetSwitching,
+      true,
+      "the target destruction is flagged as target switching"
+    );
+  } else {
+    await waitFor(
+      () => targets.length == 2,
+      "Wait for all expected targets after navigation"
+    );
+    is(
+      destroyedTargets.length,
+      1,
+      "with JSWindowActor based target, the top level target is destroyed"
+    );
+    is(
+      targetCommand.targetFront,
+      targets[1].targetFront,
+      "we got a new target"
+    );
+    ok(
+      !targetCommand.targetFront.isDestroyed(),
+      "that target is not destroyed"
+    );
+    ok(
+      targets[0].targetFront.isDestroyed(),
+      "but the previous one is destroyed"
+    );
+  }
+
+  await onNewTargetProcessed;
+
+  targetCommand.unwatchTargets({ types: [TYPES.FRAME], onAvailable });
+
+  targetCommand.destroy();
+
+  BrowserTestUtils.removeTab(tab);
+
+  await commands.destroy();
+}
+
+async function testNestedIframes() {
+  info("Test TargetCommand against nested frames");
+
+  const nestedIframeUrl = `https://example.com/document-builder.sjs?html=${encodeURIComponent(
+    "<title>second</title><h3>second level iframe</h3>"
+  )}&delay=500`;
+
+  const testUrl = `data:text/html;charset=utf-8,
+    <h1>Top-level</h1>
+    <iframe id=first-level
+      src='data:text/html;charset=utf-8,${encodeURIComponent(
+        `<title>first</title><h2>first level iframe</h2><iframe id=second-level src="${nestedIframeUrl}"></iframe>`
+      )}'
+    ></iframe>`;
+
+  // Create a TargetCommand for a given test tab
+  const tab = await addTab(testUrl);
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Check that calling getAllTargets([frame]) return the same target instances
+  const frames = await targetCommand.getAllTargets([TYPES.FRAME]);
+
+  is(frames[0], targetCommand.targetFront, "First target is the top level one");
+  const topParent = await frames[0].getParentTarget();
+  is(topParent, null, "Top level target has no parent");
+
+  if (isEveryFrameTargetEnabled()) {
+    const firstIframeTarget = frames.find(target => target.title == "first");
+    ok(
+      firstIframeTarget,
+      "With EFT, got the target for the first level iframe"
+    );
+    const firstParent = await firstIframeTarget.getParentTarget();
+    is(
+      firstParent,
+      targetCommand.targetFront,
+      "With EFT, first level has top level target as parent"
+    );
+
+    const secondIframeTarget = frames.find(target => target.title == "second");
+    ok(secondIframeTarget, "Got the target for the second level iframe");
+    const secondParent = await secondIframeTarget.getParentTarget();
+    is(
+      secondParent,
+      firstIframeTarget,
+      "With EFT, second level has the first level target as parent"
+    );
+  } else if (isFissionEnabled()) {
+    const secondIframeTarget = frames.find(target => target.title == "second");
+    ok(secondIframeTarget, "Got the target for the second level iframe");
+    const secondParent = await secondIframeTarget.getParentTarget();
+    is(
+      secondParent,
+      targetCommand.targetFront,
+      "With fission, second level has top level target as parent"
+    );
+  }
+
+  await commands.destroy();
+}
diff --git a/devtools/shared/commands/target/tests/browser_target_command_frames_popups.js b/devtools/shared/commands/target/tests/browser_target_command_frames_popups.js
new file mode 100644
index 0000000000..68f7244671
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_frames_popups.js
@@ -0,0 +1,168 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that we create targets for popups
+
+const TEST_URL = "https://example.org/document-builder.sjs?html=main page";
+const POPUP_URL = "https://example.com/document-builder.sjs?html=popup";
+const POPUP_SECOND_URL =
+  "https://example.com/document-builder.sjs?html=popup-navigated";
+
+add_task(async function () {
+  await pushPref("devtools.popups.debug", true);
+  // We expect to create a target for a same-process iframe
+  // in the test against window.open to load a document in an iframe.
+  await pushPref("devtools.every-frame-target.enabled", true);
+
+  // Create a TargetCommand for a given test tab
+  const tab = await addTab(TEST_URL);
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Assert that watchTargets will call the create callback for all existing frames
+  const targets = [];
+  const destroyedTargets = [];
+  const onAvailable = ({ targetFront }) => {
+    targets.push(targetFront);
+  };
+  const onDestroyed = ({ targetFront }) => {
+    destroyedTargets.push(targetFront);
+  };
+  await targetCommand.watchTargets({
+    types: [TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+
+  is(targets.length, 1, "At first, we only get one target");
+  is(
+    targets[0],
+    targetCommand.targetFront,
+    "And this target is the top level one"
+  );
+
+  info("Open a popup");
+  const firstPopupBrowsingContext = await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [POPUP_URL],
+    url => {
+      const win = content.open(url);
+      return win.browsingContext;
+    }
+  );
+
+  await waitFor(() => targets.length === 2);
+  ok(true, "We are notified about the first popup's target");
+
+  is(
+    targets[1].browsingContextID,
+    firstPopupBrowsingContext.id,
+    "the new target is for the popup"
+  );
+  is(targets[1].url, POPUP_URL, "the new target has the right url");
+
+  info("Navigate the popup to a second location");
+  await SpecialPowers.spawn(
+    firstPopupBrowsingContext,
+    [POPUP_SECOND_URL],
+    url => {
+      content.location.href = url;
+    }
+  );
+
+  await waitFor(() => targets.length === 3);
+  ok(true, "We are notified about the new location popup's target");
+
+  await waitFor(() => destroyedTargets.length === 1);
+  ok(true, "The first popup's target is destroyed");
+  is(
+    destroyedTargets[0],
+    targets[1],
+    "The destroyed target is the popup's one"
+  );
+
+  is(
+    targets[2].browsingContextID,
+    firstPopupBrowsingContext.id,
+    "the new location target is for the popup"
+  );
+  is(
+    targets[2].url,
+    POPUP_SECOND_URL,
+    "the new location target has the right url"
+  );
+
+  info("Close the popup");
+  await SpecialPowers.spawn(firstPopupBrowsingContext, [], () => {
+    content.close();
+  });
+
+  await waitFor(() => destroyedTargets.length === 2);
+  ok(true, "The popup's target is destroyed");
+  is(
+    destroyedTargets[1],
+    targets[2],
+    "The destroyed target is the popup's one"
+  );
+
+  info("Open a about:blank popup");
+  const aboutBlankPopupBrowsingContext = await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [],
+    () => {
+      const win = content.open("about:blank");
+      return win.browsingContext;
+    }
+  );
+
+  await waitFor(() => targets.length === 4);
+  ok(true, "We are notified about the about:blank popup's target");
+
+  is(
+    targets[3].browsingContextID,
+    aboutBlankPopupBrowsingContext.id,
+    "the new target is for the popup"
+  );
+  is(targets[3].url, "about:blank", "the new target has the right url");
+
+  info("Select the original tab and reload it");
+  gBrowser.selectedTab = tab;
+  await BrowserTestUtils.reloadTab(tab);
+
+  await waitFor(() => targets.length === 5);
+  is(targets[4], targetCommand.targetFront, "We get a new top level target");
+  ok(!targets[3].isDestroyed(), "The about:blank popup target is still alive");
+
+  info("Call about:blank popup method to ensure it really is functional");
+  await targets[3].logInPage("foo");
+
+  info(
+    "Ensure that iframe using window.open to load their document aren't considered as popups"
+  );
+  await SpecialPowers.spawn(gBrowser.selectedBrowser, [], async () => {
+    const iframe = content.document.createElement("iframe");
+    iframe.setAttribute("name", "test-iframe");
+    content.document.documentElement.appendChild(iframe);
+    content.open("data:text/html,iframe", "test-iframe");
+  });
+  await waitFor(() => targets.length === 6);
+  is(
+    targets[5].targetForm.isPopup,
+    false,
+    "The iframe target isn't considered as a popup"
+  );
+
+  targetCommand.unwatchTargets({
+    types: [TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+  targetCommand.destroy();
+  BrowserTestUtils.removeTab(tab);
+  await commands.destroy();
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_frames_reload_server_side_targets.js b/devtools/shared/commands/target/tests/browser_target_command_frames_reload_server_side_targets.js
new file mode 100644
index 0000000000..d05ff5a962
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_frames_reload_server_side_targets.js
@@ -0,0 +1,104 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that the framework handles reloading a document with multiple remote frames (See Bug 1724909).
+
+const REMOTE_ORIGIN = "https://example.com/";
+const REMOTE_IFRAME_URL_1 =
+  REMOTE_ORIGIN + "/document-builder.sjs?html=first_remote_iframe";
+const REMOTE_IFRAME_URL_2 =
+  REMOTE_ORIGIN + "/document-builder.sjs?html=second_remote_iframe";
+const TEST_URL =
+  "https://example.org/document-builder.sjs?html=org" +
+  `<iframe src=${REMOTE_IFRAME_URL_1}></iframe>` +
+  `<iframe src=${REMOTE_IFRAME_URL_2}></iframe>`;
+
+add_task(async function () {
+  // Create a TargetCommand for a given test tab
+  const tab = await addTab(TEST_URL);
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Assert that watchTargets will call the create callback for all existing frames
+  const targets = [];
+  const destroyedTargets = [];
+  const onAvailable = ({ targetFront }) => {
+    targets.push(targetFront);
+  };
+  const onDestroyed = ({ targetFront }) => {
+    destroyedTargets.push(targetFront);
+  };
+  await targetCommand.watchTargets({
+    types: [TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+
+  await waitFor(() => targets.length === 3);
+  ok(
+    true,
+    "We are notified about the top-level document and the 2 remote iframes"
+  );
+
+  info("Reload the page");
+  // When a new target will be created, we need to wait until it's fully processed
+  // to avoid pending promises.
+  const onNewTargetProcessed = targetCommand.once("processed-available-target");
+  gBrowser.reloadTab(tab);
+  await onNewTargetProcessed;
+
+  await waitFor(() => targets.length === 6 && destroyedTargets.length === 3);
+
+  // Get the previous targets in a dedicated array and remove them from `targets`
+  const previousTargets = targets.splice(0, 3);
+  ok(
+    previousTargets.every(targetFront => targetFront.isDestroyed()),
+    "The previous targets are all destroyed"
+  );
+  ok(
+    targets.every(targetFront => !targetFront.isDestroyed()),
+    "The new targets are not destroyed"
+  );
+
+  info("Reload one of the iframe");
+  SpecialPowers.spawn(tab.linkedBrowser, [], () => {
+    const iframeEl = content.document.querySelector("iframe");
+    SpecialPowers.spawn(iframeEl.browsingContext, [], () => {
+      content.document.location.reload();
+    });
+  });
+  await waitFor(
+    () =>
+      targets.length + previousTargets.length === 7 &&
+      destroyedTargets.length === 4
+  );
+  const iframeTarget = targets.find(t => t === destroyedTargets.at(-1));
+  ok(iframeTarget, "Got the iframe target that got destroyed");
+  for (const target of targets) {
+    if (target == iframeTarget) {
+      ok(
+        target.isDestroyed(),
+        "The iframe target we navigated from is destroyed"
+      );
+    } else {
+      ok(
+        !target.isDestroyed(),
+        `Target ${target.actorID}|${target.url} isn't destroyed`
+      );
+    }
+  }
+
+  targetCommand.unwatchTargets({
+    types: [TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+  targetCommand.destroy();
+  BrowserTestUtils.removeTab(tab);
+  await commands.destroy();
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_getAllTargets.js b/devtools/shared/commands/target/tests/browser_target_command_getAllTargets.js
new file mode 100644
index 0000000000..a7d5e51b3c
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_getAllTargets.js
@@ -0,0 +1,119 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API getAllTargets.
+
+const FISSION_TEST_URL = URL_ROOT_SSL + "fission_document.html";
+const CHROME_WORKER_URL = CHROME_URL_ROOT + "test_worker.js";
+
+add_task(async function () {
+  // Disable the preloaded process as it creates processes intermittently
+  // which forces the emission of RDP requests we aren't correctly waiting for.
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+
+  info("Setup the test page with workers of all types");
+
+  const tab = await addTab(FISSION_TEST_URL);
+
+  // Instantiate a worker in the parent process
+  // eslint-disable-next-line no-unused-vars
+  const worker = new Worker(CHROME_WORKER_URL + "#simple-worker");
+  // eslint-disable-next-line no-unused-vars
+  const sharedWorker = new SharedWorker(CHROME_WORKER_URL + "#shared-worker");
+
+  info("Create a target list for the main process target");
+  const commands = await CommandsFactory.forMainProcess();
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+  await targetCommand.startListening();
+
+  info("Check getAllTargets will throw when providing invalid arguments");
+  Assert.throws(
+    () => targetCommand.getAllTargets(),
+    e => e.message === "getAllTargets expects a non-empty array of types"
+  );
+
+  Assert.throws(
+    () => targetCommand.getAllTargets([]),
+    e => e.message === "getAllTargets expects a non-empty array of types"
+  );
+
+  info("Check getAllTargets returns consistent results with several types");
+  const workerTargets = targetCommand.getAllTargets([TYPES.WORKER]);
+  const serviceWorkerTargets = targetCommand.getAllTargets([
+    TYPES.SERVICE_WORKER,
+  ]);
+  const sharedWorkerTargets = targetCommand.getAllTargets([
+    TYPES.SHARED_WORKER,
+  ]);
+  const processTargets = targetCommand.getAllTargets([TYPES.PROCESS]);
+  const frameTargets = targetCommand.getAllTargets([TYPES.FRAME]);
+
+  const allWorkerTargetsReference = [
+    ...workerTargets,
+    ...serviceWorkerTargets,
+    ...sharedWorkerTargets,
+  ];
+  const allWorkerTargets = targetCommand.getAllTargets([
+    TYPES.WORKER,
+    TYPES.SERVICE_WORKER,
+    TYPES.SHARED_WORKER,
+  ]);
+
+  is(
+    allWorkerTargets.length,
+    allWorkerTargetsReference.length,
+    "getAllTargets([worker, service, shared]) returned the expected number of targets"
+  );
+
+  ok(
+    allWorkerTargets.every(t => allWorkerTargetsReference.includes(t)),
+    "getAllTargets([worker, service, shared]) returned the expected targets"
+  );
+
+  const allTargetsReference = [
+    ...allWorkerTargets,
+    ...processTargets,
+    ...frameTargets,
+  ];
+  const allTargets = targetCommand.getAllTargets(targetCommand.ALL_TYPES);
+  is(
+    allTargets.length,
+    allTargetsReference.length,
+    "getAllTargets(ALL_TYPES) returned the expected number of targets"
+  );
+
+  ok(
+    allTargets.every(t => allTargetsReference.includes(t)),
+    "getAllTargets(ALL_TYPES) returned the expected targets"
+  );
+
+  for (const target of allTargets) {
+    is(
+      target.commands,
+      commands,
+      "Each target front has a `commands` attribute - " + target
+    );
+  }
+
+  // Wait for all the targets to be fully attached so we don't have pending requests.
+  await waitForAllTargetsToBeAttached(targetCommand);
+
+  ok(
+    !targetCommand.isDestroyed(),
+    "TargetCommand isn't destroyed before calling commands.destroy()"
+  );
+  await commands.destroy();
+  ok(
+    targetCommand.isDestroyed(),
+    "TargetCommand is destroyed after calling commands.destroy()"
+  );
+
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    // registrationPromise is set by the test page.
+    const registration = await content.wrappedJSObject.registrationPromise;
+    registration.unregister();
+  });
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_invalid_api_usage.js b/devtools/shared/commands/target/tests/browser_target_command_invalid_api_usage.js
new file mode 100644
index 0000000000..dbdaae7f05
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_invalid_api_usage.js
@@ -0,0 +1,78 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test watch/unwatchTargets throw when provided with invalid types.
+
+const TEST_URL = "data:text/html;charset=utf-8,invalid api usage test";
+
+add_task(async function () {
+  info("Setup the test page with workers of all types");
+  const tab = await addTab(TEST_URL);
+
+  info("Create a target list for a tab target");
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+
+  const onAvailable = function () {};
+
+  await Assert.rejects(
+    targetCommand.watchTargets({ types: [null], onAvailable }),
+    /TargetCommand.watchTargets invoked with an unknown type/,
+    "watchTargets should throw for null type"
+  );
+
+  await Assert.rejects(
+    targetCommand.watchTargets({ types: [undefined], onAvailable }),
+    /TargetCommand.watchTargets invoked with an unknown type/,
+    "watchTargets should throw for undefined type"
+  );
+
+  await Assert.rejects(
+    targetCommand.watchTargets({ types: ["NOT_A_TARGET"], onAvailable }),
+    /TargetCommand.watchTargets invoked with an unknown type/,
+    "watchTargets should throw for unknown type"
+  );
+
+  await Assert.rejects(
+    targetCommand.watchTargets({
+      types: [targetCommand.TYPES.FRAME, "NOT_A_TARGET"],
+      onAvailable,
+    }),
+    /TargetCommand.watchTargets invoked with an unknown type/,
+    "watchTargets should throw for unknown type mixed with a correct type"
+  );
+
+  Assert.throws(
+    () => targetCommand.unwatchTargets({ types: [null], onAvailable }),
+    /TargetCommand.unwatchTargets invoked with an unknown type/,
+    "unwatchTargets should throw for null type"
+  );
+
+  Assert.throws(
+    () => targetCommand.unwatchTargets({ types: [undefined], onAvailable }),
+    /TargetCommand.unwatchTargets invoked with an unknown type/,
+    "unwatchTargets should throw for undefined type"
+  );
+
+  Assert.throws(
+    () =>
+      targetCommand.unwatchTargets({ types: ["NOT_A_TARGET"], onAvailable }),
+    /TargetCommand.unwatchTargets invoked with an unknown type/,
+    "unwatchTargets should throw for unknown type"
+  );
+
+  Assert.throws(
+    () =>
+      targetCommand.unwatchTargets({
+        types: [targetCommand.TYPES.CONSOLE_MESSAGE, "NOT_A_TARGET"],
+        onAvailable,
+      }),
+    /TargetCommand.unwatchTargets invoked with an unknown type/,
+    "unwatchTargets should throw for unknown type mixed with a correct type"
+  );
+
+  BrowserTestUtils.removeTab(tab);
+  await commands.destroy();
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_processes.js b/devtools/shared/commands/target/tests/browser_target_command_processes.js
new file mode 100644
index 0000000000..d9e7ec65a9
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_processes.js
@@ -0,0 +1,242 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API around processes
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," + encodeURIComponent(`<div id="test"></div>`);
+
+add_task(async function () {
+  // Enabled fission's pref as the TargetCommand is almost disabled without it
+  await pushPref("devtools.browsertoolbox.scope", "everything");
+  // Disable the preloaded process as it gets created lazily and may interfere
+  // with process count assertions
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+  // This preference helps destroying the content process when we close the tab
+  await pushPref("dom.ipc.keepProcessesAlive.web", 1);
+
+  const commands = await CommandsFactory.forMainProcess();
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  await testProcesses(targetCommand, targetCommand.targetFront);
+
+  targetCommand.destroy();
+  // Wait for all the targets to be fully attached so we don't have pending requests.
+  await Promise.all(
+    targetCommand.getAllTargets(targetCommand.ALL_TYPES).map(t => t.initialized)
+  );
+
+  await commands.destroy();
+});
+
+add_task(async function () {
+  const commands = await CommandsFactory.forMainProcess();
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const created = [];
+  const destroyed = [];
+  const onAvailable = ({ targetFront }) => {
+    created.push(targetFront);
+  };
+  const onDestroyed = ({ targetFront }) => {
+    destroyed.push(targetFront);
+  };
+  await targetCommand.watchTargets({
+    types: [targetCommand.TYPES.PROCESS],
+    onAvailable,
+    onDestroyed,
+  });
+  ok(created.length > 1, "We get many content process targets");
+
+  targetCommand.stopListening();
+
+  await waitFor(
+    () => created.length == destroyed.length,
+    "Wait for the destruction of all content process targets when calling stopListening"
+  );
+  is(
+    created.length,
+    destroyed.length,
+    "Got notification of destruction for all previously reported targets"
+  );
+
+  targetCommand.destroy();
+  // Wait for all the targets to be fully attached so we don't have pending requests.
+  await Promise.all(
+    targetCommand.getAllTargets(targetCommand.ALL_TYPES).map(t => t.initialized)
+  );
+
+  await commands.destroy();
+});
+
+async function testProcesses(targetCommand, target) {
+  info("Test TargetCommand against processes");
+  const { TYPES } = targetCommand;
+
+  // Note that ppmm also includes the parent process, which is considered as a frame rather than a process
+  const originalProcessesCount = Services.ppmm.childCount - 1;
+  const processes = await targetCommand.getAllTargets([TYPES.PROCESS]);
+  is(
+    processes.length,
+    originalProcessesCount,
+    "Get a target for all content processes"
+  );
+
+  const processes2 = await targetCommand.getAllTargets([TYPES.PROCESS]);
+  is(
+    processes2.length,
+    originalProcessesCount,
+    "retrieved the same number of processes"
+  );
+  function sortFronts(f1, f2) {
+    return f1.actorID < f2.actorID;
+  }
+  processes.sort(sortFronts);
+  processes2.sort(sortFronts);
+  for (let i = 0; i < processes.length; i++) {
+    is(processes[i], processes2[i], `process ${i} targets are the same`);
+  }
+
+  // Assert that watchTargets will call the create callback for all existing frames
+  const targets = new Set();
+
+  const pidRegExp = /^\d+$/;
+
+  const onAvailable = ({ targetFront }) => {
+    if (targets.has(targetFront)) {
+      ok(false, "The same target is notified multiple times via onAvailable");
+    }
+    is(
+      targetFront.targetType,
+      TYPES.PROCESS,
+      "We are only notified about process targets"
+    );
+    ok(
+      targetFront == target ? targetFront.isTopLevel : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
+    );
+    ok(
+      pidRegExp.test(targetFront.processID),
+      `Target has processID of expected shape (${targetFront.processID})`
+    );
+    targets.add(targetFront);
+  };
+  const onDestroyed = ({ targetFront }) => {
+    if (!targets.has(targetFront)) {
+      ok(
+        false,
+        "A target is declared destroyed via onDestroy without being notified via onAvailable"
+      );
+    }
+    is(
+      targetFront.targetType,
+      TYPES.PROCESS,
+      "We are only notified about process targets"
+    );
+    ok(
+      !targetFront.isTopLevel,
+      "We are never notified about the top level target destruction"
+    );
+    targets.delete(targetFront);
+  };
+  await targetCommand.watchTargets({
+    types: [TYPES.PROCESS],
+    onAvailable,
+    onDestroyed,
+  });
+  is(
+    targets.size,
+    originalProcessesCount,
+    "retrieved the same number of processes via watchTargets"
+  );
+  for (let i = 0; i < processes.length; i++) {
+    ok(
+      targets.has(processes[i]),
+      `process ${i} targets are the same via watchTargets`
+    );
+  }
+
+  const previousTargets = new Set(targets);
+  // Assert that onAvailable is called for processes created *after* the call to watchTargets
+  const onProcessCreated = new Promise(resolve => {
+    const onAvailable2 = ({ targetFront }) => {
+      if (previousTargets.has(targetFront)) {
+        return;
+      }
+      targetCommand.unwatchTargets({
+        types: [TYPES.PROCESS],
+        onAvailable: onAvailable2,
+      });
+      resolve(targetFront);
+    };
+    targetCommand.watchTargets({
+      types: [TYPES.PROCESS],
+      onAvailable: onAvailable2,
+    });
+  });
+  const tab1 = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    url: TEST_URL,
+    forceNewProcess: true,
+  });
+  const createdTarget = await onProcessCreated;
+  // For some reason, creating a new tab purges processes created from previous tests
+  // so it is not reasonable to assert the size of `targets` as it may be lower than expected.
+  ok(targets.has(createdTarget), "The new tab process is in the list");
+
+  const processCountAfterTabOpen = targets.size;
+
+  // Assert that onDestroy is called for destroyed processes
+  const onProcessDestroyed = new Promise(resolve => {
+    const onAvailable3 = () => {};
+    const onDestroyed3 = ({ targetFront }) => {
+      resolve(targetFront);
+      targetCommand.unwatchTargets({
+        types: [TYPES.PROCESS],
+        onAvailable: onAvailable3,
+        onDestroyed: onDestroyed3,
+      });
+    };
+    targetCommand.watchTargets({
+      types: [TYPES.PROCESS],
+      onAvailable: onAvailable3,
+      onDestroyed: onDestroyed3,
+    });
+  });
+
+  BrowserTestUtils.removeTab(tab1);
+
+  const destroyedTarget = await onProcessDestroyed;
+  is(
+    targets.size,
+    processCountAfterTabOpen - 1,
+    "The closed tab's process has been reported as destroyed"
+  );
+  ok(
+    !targets.has(destroyedTarget),
+    "The destroyed target is no longer in the list"
+  );
+  is(
+    destroyedTarget,
+    createdTarget,
+    "The destroyed target is the one that has been reported as created"
+  );
+
+  targetCommand.unwatchTargets({
+    types: [TYPES.PROCESS],
+    onAvailable,
+    onDestroyed,
+  });
+
+  // Ensure that getAllTargets still works after the call to unwatchTargets
+  const processes3 = await targetCommand.getAllTargets([TYPES.PROCESS]);
+  is(
+    processes3.length,
+    processCountAfterTabOpen - 1,
+    "getAllTargets reports a new target"
+  );
+}
diff --git a/devtools/shared/commands/target/tests/browser_target_command_reload.js b/devtools/shared/commands/target/tests/browser_target_command_reload.js
new file mode 100644
index 0000000000..9d8cacd23d
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_reload.js
@@ -0,0 +1,115 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand's reload method
+//
+// Note that we reload against main process,
+// but this is hard/impossible to test as it reloads the test script itself
+// and so stops its execution.
+
+// Load a page with a JS script that change its value everytime we load it
+// (that's to see if the reload loads from cache or not)
+const TEST_URL = URL_ROOT + "incremental-js-value-script.sjs";
+
+add_task(async function () {
+  info(" ### Test reloading a Tab");
+
+  // Create a TargetCommand for a given test tab
+  const tab = await addTab(TEST_URL);
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+
+  // We have to start listening in order to ensure having a targetFront available
+  await targetCommand.startListening();
+
+  const firstJSValue = await getContentVariable();
+  is(firstJSValue, "1", "Got an initial value for the JS variable");
+
+  const onReloaded = BrowserTestUtils.browserLoaded(gBrowser.selectedBrowser);
+  await targetCommand.reloadTopLevelTarget();
+  info("Wait for the tab to be reloaded");
+  await onReloaded;
+
+  const secondJSValue = await getContentVariable();
+  is(
+    secondJSValue,
+    "1",
+    "The first reload didn't bypass the cache, so the JS Script is the same and we got the same value"
+  );
+
+  const onSecondReloaded = BrowserTestUtils.browserLoaded(
+    gBrowser.selectedBrowser
+  );
+  await targetCommand.reloadTopLevelTarget(true);
+  info("Wait for the tab to be reloaded");
+  await onSecondReloaded;
+
+  // The value is 3 and not 2, because we got a HTTP request, but it returned 304 and the browser fetched his cached content
+  const thirdJSValue = await getContentVariable();
+  is(
+    thirdJSValue,
+    "3",
+    "The second reload did bypass the cache, so the JS Script is different and we got a new value"
+  );
+
+  BrowserTestUtils.removeTab(tab);
+
+  await commands.destroy();
+});
+
+add_task(async function () {
+  info(" ### Test reloading an Add-on");
+
+  const extension = ExtensionTestUtils.loadExtension({
+    useAddonManager: "temporary",
+    background() {
+      const { browser } = this;
+      browser.test.log("background script executed");
+    },
+  });
+
+  await extension.startup();
+
+  const commands = await CommandsFactory.forAddon(extension.id);
+  const targetCommand = commands.targetCommand;
+
+  // We have to start listening in order to ensure having a targetFront available
+  await targetCommand.startListening();
+
+  const { onResource: onReloaded } =
+    await commands.resourceCommand.waitForNextResource(
+      commands.resourceCommand.TYPES.DOCUMENT_EVENT,
+      {
+        ignoreExistingResources: true,
+        predicate(resource) {
+          return resource.name == "dom-loading";
+        },
+      }
+    );
+
+  const backgroundPageURL = targetCommand.targetFront.url;
+  ok(backgroundPageURL, "Got the background page URL");
+  await targetCommand.reloadTopLevelTarget();
+
+  info("Wait for next dom-loading DOCUMENT_EVENT");
+  const event = await onReloaded;
+
+  // If we get about:blank here, it most likely means we receive notification
+  // for the previous background page being unload and navigating to about:blank
+  is(
+    event.url,
+    backgroundPageURL,
+    "We received the DOCUMENT_EVENT's for the expected document: the new background page."
+  );
+
+  await commands.destroy();
+
+  await extension.unload();
+});
+function getContentVariable() {
+  return SpecialPowers.spawn(gBrowser.selectedBrowser, [], function () {
+    return content.wrappedJSObject.jsValue;
+  });
+}
diff --git a/devtools/shared/commands/target/tests/browser_target_command_scope_flag.js b/devtools/shared/commands/target/tests/browser_target_command_scope_flag.js
new file mode 100644
index 0000000000..f07a6aaac3
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_scope_flag.js
@@ -0,0 +1,190 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API with changes made to devtools.browsertoolbox.scope
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," + encodeURIComponent(`<div id="test"></div>`);
+
+add_task(async function () {
+  // Do not run this test when both fission and EFT is disabled as it changes
+  // the number of targets
+  if (!isFissionEnabled() && !isEveryFrameTargetEnabled()) {
+    return;
+  }
+
+  // Disable the preloaded process as it gets created lazily and may interfere
+  // with process count assertions
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+  // This preference helps destroying the content process when we close the tab
+  await pushPref("dom.ipc.keepProcessesAlive.web", 1);
+
+  // First test with multiprocess debugging enabled
+  await pushPref("devtools.browsertoolbox.scope", "everything");
+
+  const commands = await CommandsFactory.forMainProcess();
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+  const { TYPES } = targetCommand;
+
+  const targets = new Set();
+  const destroyedTargetIsModeSwitchingMap = new Map();
+  const onAvailable = async ({ targetFront }) => {
+    targets.add(targetFront);
+  };
+  const onDestroyed = ({ targetFront, isModeSwitching }) => {
+    destroyedTargetIsModeSwitchingMap.set(targetFront, isModeSwitching);
+    targets.delete(targetFront);
+  };
+  await targetCommand.watchTargets({
+    types: [TYPES.PROCESS, TYPES.FRAME],
+    onAvailable,
+    onDestroyed,
+  });
+  ok(targets.size > 1, "We get many targets");
+
+  info("Open a tab in a new content process");
+  await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    url: TEST_URL,
+    forceNewProcess: true,
+  });
+
+  const newTabProcessID =
+    gBrowser.selectedTab.linkedBrowser.browsingContext.currentWindowGlobal
+      .osPid;
+  const newTabInnerWindowId =
+    gBrowser.selectedTab.linkedBrowser.browsingContext.currentWindowGlobal
+      .innerWindowId;
+
+  info("Wait for the tab content process target");
+  const processTarget = await waitFor(() =>
+    [...targets].find(
+      target =>
+        target.targetType == TYPES.PROCESS &&
+        target.processID == newTabProcessID
+    )
+  );
+
+  info("Wait for the tab window global target");
+  const windowGlobalTarget = await waitFor(() =>
+    [...targets].find(
+      target =>
+        target.targetType == TYPES.FRAME &&
+        target.innerWindowId == newTabInnerWindowId
+    )
+  );
+
+  let multiprocessTargetCount = targets.size;
+
+  info("Disable multiprocess debugging");
+  await pushPref("devtools.browsertoolbox.scope", "parent-process");
+
+  info("Wait for all targets but top level and workers to be destroyed");
+  await waitFor(() =>
+    [...targets].every(
+      target =>
+        target == targetCommand.targetFront || target.targetType == TYPES.WORKER
+    )
+  );
+
+  ok(processTarget.isDestroyed(), "The process target is destroyed");
+  ok(
+    destroyedTargetIsModeSwitchingMap.get(processTarget),
+    "isModeSwitching was passed to onTargetDestroyed and is true for the process target"
+  );
+  ok(windowGlobalTarget.isDestroyed(), "The window global target is destroyed");
+  ok(
+    destroyedTargetIsModeSwitchingMap.get(windowGlobalTarget),
+    "isModeSwitching was passed to onTargetDestroyed and is true for the window global target"
+  );
+
+  info("Open a second tab in a new content process");
+  const parentProcessTargetCount = targets.size;
+  await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    url: TEST_URL,
+    forceNewProcess: true,
+  });
+
+  await wait(1000);
+  is(
+    parentProcessTargetCount,
+    targets.size,
+    "The new tab process should be ignored and no target be created"
+  );
+
+  info("Re-enable multiprocess debugging");
+  await pushPref("devtools.browsertoolbox.scope", "everything");
+
+  // The second tab relates to one content process target and one window global target
+  multiprocessTargetCount += 2;
+
+  await waitFor(
+    () => targets.size == multiprocessTargetCount,
+    "Wait for all targets we used to have before disable multiprocess debugging"
+  );
+
+  info("Wait for the tab content process target to be available again");
+  ok(
+    [...targets].some(
+      target =>
+        target.targetType == TYPES.PROCESS &&
+        target.processID == newTabProcessID
+    ),
+    "We have the tab content process target"
+  );
+
+  info("Wait for the tab window global target to be available again");
+  ok(
+    [...targets].some(
+      target =>
+        target.targetType == TYPES.FRAME &&
+        target.innerWindowId == newTabInnerWindowId
+    ),
+    "We have the tab window global target"
+  );
+
+  info("Open a third tab in a new content process");
+  await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    url: TEST_URL,
+    forceNewProcess: true,
+  });
+
+  const thirdTabProcessID =
+    gBrowser.selectedTab.linkedBrowser.browsingContext.currentWindowGlobal
+      .osPid;
+  const thirdTabInnerWindowId =
+    gBrowser.selectedTab.linkedBrowser.browsingContext.currentWindowGlobal
+      .innerWindowId;
+
+  info("Wait for the third tab content process target");
+  await waitFor(() =>
+    [...targets].find(
+      target =>
+        target.targetType == TYPES.PROCESS &&
+        target.processID == thirdTabProcessID
+    )
+  );
+
+  info("Wait for the third tab window global target");
+  await waitFor(() =>
+    [...targets].find(
+      target =>
+        target.targetType == TYPES.FRAME &&
+        target.innerWindowId == thirdTabInnerWindowId
+    )
+  );
+
+  targetCommand.destroy();
+
+  // Wait for all the targets to be fully attached so we don't have pending requests.
+  await Promise.all(
+    targetCommand.getAllTargets(targetCommand.ALL_TYPES).map(t => t.initialized)
+  );
+
+  await commands.destroy();
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_service_workers.js b/devtools/shared/commands/target/tests/browser_target_command_service_workers.js
new file mode 100644
index 0000000000..d71401fd8c
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_service_workers.js
@@ -0,0 +1,77 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API for service workers in content tabs.
+
+const FISSION_TEST_URL = URL_ROOT_SSL + "fission_document.html";
+
+add_task(async function () {
+  // Disable the preloaded process as it creates processes intermittently
+  // which forces the emission of RDP requests we aren't correctly waiting for.
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+
+  info("Setup the test page with workers of all types");
+
+  const tab = await addTab(FISSION_TEST_URL);
+
+  info("Create a target list for a tab target");
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  // Enable Service Worker listening.
+  targetCommand.listenForServiceWorkers = true;
+  await targetCommand.startListening();
+
+  const serviceWorkerTargets = targetCommand.getAllTargets([
+    TYPES.SERVICE_WORKER,
+  ]);
+  is(
+    serviceWorkerTargets.length,
+    1,
+    "TargetCommmand has 1 service worker target"
+  );
+
+  info("Check that the onAvailable is done when watchTargets resolves");
+  const targets = [];
+  const onAvailable = async ({ targetFront }) => {
+    // Wait for one second here to check that watch targets waits for
+    // the onAvailable callbacks correctly.
+    await wait(1000);
+    targets.push(targetFront);
+  };
+  const onDestroyed = ({ targetFront }) =>
+    targets.splice(targets.indexOf(targetFront), 1);
+
+  await targetCommand.watchTargets({
+    types: [TYPES.SERVICE_WORKER],
+    onAvailable,
+    onDestroyed,
+  });
+
+  // We expect onAvailable to have been called one time, for the only service
+  // worker target available in the test page.
+  is(targets.length, 1, "onAvailable has resolved");
+  is(
+    targets[0],
+    serviceWorkerTargets[0],
+    "onAvailable was called with the expected service worker target"
+  );
+
+  info("Unregister the worker and wait until onDestroyed is called.");
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    // registrationPromise is set by the test page.
+    const registration = await content.wrappedJSObject.registrationPromise;
+    registration.unregister();
+  });
+  await waitUntil(() => targets.length === 0);
+
+  // Stop listening to avoid worker related requests
+  targetCommand.destroy();
+
+  await commands.waitForRequestsToSettle();
+
+  await commands.destroy();
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_service_workers_navigation.js b/devtools/shared/commands/target/tests/browser_target_command_service_workers_navigation.js
new file mode 100644
index 0000000000..caf95f11c2
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_service_workers_navigation.js
@@ -0,0 +1,389 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API for service workers when navigating in content tabs.
+// When the top level target navigates, we manually call onTargetAvailable for
+// service workers which now match the page domain. We assert that the callbacks
+// will be called the expected number of times here.
+
+const COM_PAGE_URL = URL_ROOT_SSL + "test_sw_page.html";
+const COM_WORKER_URL = URL_ROOT_SSL + "test_sw_page_worker.js";
+const ORG_PAGE_URL = URL_ROOT_ORG_SSL + "test_sw_page.html";
+const ORG_WORKER_URL = URL_ROOT_ORG_SSL + "test_sw_page_worker.js";
+
+/**
+ * This test will navigate between two pages, both controlled by different
+ * service workers.
+ *
+ * The steps will be:
+ * - navigate to .com page
+ * - create target list
+ * - navigate to .org page
+ * - reload .org page
+ * - unregister .org worker
+ * - navigate back to .com page
+ * - unregister .com worker
+ *
+ * First we test this with destroyServiceWorkersOnNavigation = false.
+ * In this case we expect the following calls:
+ * - navigate to .com page
+ * - create target list
+ *   - onAvailable should be called for the .com worker
+ * - navigate to .org page
+ *   - onAvailable should be called for the .org worker
+ * - reload .org page
+ *   - nothing should happen
+ * - unregister .org worker
+ *   - onDestroyed should be called for the .org worker
+ * - navigate back to .com page
+ *   - nothing should happen
+ * - unregister .com worker
+ *   - onDestroyed should be called for the .com worker
+ */
+add_task(async function test_NavigationBetweenTwoDomains_NoDestroy() {
+  await setupServiceWorkerNavigationTest();
+
+  const tab = await addTab(COM_PAGE_URL);
+
+  const { hooks, commands, targetCommand } = await watchServiceWorkerTargets({
+    tab,
+    destroyServiceWorkersOnNavigation: false,
+  });
+
+  // We expect onAvailable to have been called one time, for the only service
+  // worker target available in the test page.
+  await checkHooks(hooks, {
+    available: 1,
+    destroyed: 0,
+    targets: [COM_WORKER_URL],
+  });
+
+  info("Go to .org page, wait for onAvailable to be called");
+  BrowserTestUtils.loadURIString(gBrowser.selectedBrowser, ORG_PAGE_URL);
+  await checkHooks(hooks, {
+    available: 2,
+    destroyed: 0,
+    targets: [COM_WORKER_URL, ORG_WORKER_URL],
+  });
+
+  info("Reload .org page, onAvailable and onDestroyed should not be called");
+  await BrowserTestUtils.reloadTab(gBrowser.selectedTab);
+  await checkHooks(hooks, {
+    available: 2,
+    destroyed: 0,
+    targets: [COM_WORKER_URL, ORG_WORKER_URL],
+  });
+
+  info("Unregister .org service worker and wait until onDestroyed is called.");
+  await unregisterServiceWorker(tab, ORG_PAGE_URL);
+  await checkHooks(hooks, {
+    available: 2,
+    destroyed: 1,
+    targets: [COM_WORKER_URL],
+  });
+
+  info("Go back to .com page");
+  const onBrowserLoaded = BrowserTestUtils.browserLoaded(
+    gBrowser.selectedBrowser
+  );
+  BrowserTestUtils.loadURIString(gBrowser.selectedBrowser, COM_PAGE_URL);
+  await onBrowserLoaded;
+  await checkHooks(hooks, {
+    available: 2,
+    destroyed: 1,
+    targets: [COM_WORKER_URL],
+  });
+
+  info("Unregister .com service worker and wait until onDestroyed is called.");
+  await unregisterServiceWorker(tab, COM_PAGE_URL);
+  await checkHooks(hooks, { available: 2, destroyed: 2, targets: [] });
+
+  // Stop listening to avoid worker related requests
+  targetCommand.destroy();
+
+  await commands.waitForRequestsToSettle();
+  await commands.destroy();
+  await removeTab(tab);
+});
+
+/**
+ * Same scenario as test_NavigationBetweenTwoDomains_NoDestroy, but this time
+ * with destroyServiceWorkersOnNavigation set to true.
+ *
+ * In this case we expect the following calls:
+ * - navigate to .com page
+ * - create target list
+ *   - onAvailable should be called for the .com worker
+ * - navigate to .org page
+ *   - onDestroyed should be called for the .com worker
+ *   - onAvailable should be called for the .org worker
+ * - reload .org page
+ *   - onDestroyed & onAvailable should be called for the .org worker
+ * - unregister .org worker
+ *   - onDestroyed should be called for the .org worker
+ * - navigate back to .com page
+ *   - onAvailable should be called for the .com worker
+ * - unregister .com worker
+ *   - onDestroyed should be called for the .com worker
+ */
+add_task(async function test_NavigationBetweenTwoDomains_WithDestroy() {
+  await setupServiceWorkerNavigationTest();
+
+  const tab = await addTab(COM_PAGE_URL);
+
+  const { hooks, commands, targetCommand } = await watchServiceWorkerTargets({
+    tab,
+    destroyServiceWorkersOnNavigation: true,
+  });
+
+  // We expect onAvailable to have been called one time, for the only service
+  // worker target available in the test page.
+  await checkHooks(hooks, {
+    available: 1,
+    destroyed: 0,
+    targets: [COM_WORKER_URL],
+  });
+
+  info("Go to .org page, wait for onAvailable to be called");
+  BrowserTestUtils.loadURIString(gBrowser.selectedBrowser, ORG_PAGE_URL);
+  await checkHooks(hooks, {
+    available: 2,
+    destroyed: 1,
+    targets: [ORG_WORKER_URL],
+  });
+
+  info("Reload .org page, onAvailable and onDestroyed should be called");
+  gBrowser.reloadTab(gBrowser.selectedTab);
+  await checkHooks(hooks, {
+    available: 3,
+    destroyed: 2,
+    targets: [ORG_WORKER_URL],
+  });
+
+  info("Unregister .org service worker and wait until onDestroyed is called.");
+  await unregisterServiceWorker(tab, ORG_PAGE_URL);
+  await checkHooks(hooks, { available: 3, destroyed: 3, targets: [] });
+
+  info("Go back to page 1, wait for onDestroyed and onAvailable to be called");
+  BrowserTestUtils.loadURIString(gBrowser.selectedBrowser, COM_PAGE_URL);
+  await checkHooks(hooks, {
+    available: 4,
+    destroyed: 3,
+    targets: [COM_WORKER_URL],
+  });
+
+  info("Unregister .com service worker and wait until onDestroyed is called.");
+  await unregisterServiceWorker(tab, COM_PAGE_URL);
+  await checkHooks(hooks, { available: 4, destroyed: 4, targets: [] });
+
+  // Stop listening to avoid worker related requests
+  targetCommand.destroy();
+
+  await commands.waitForRequestsToSettle();
+  await commands.destroy();
+  await removeTab(tab);
+});
+
+/**
+ * In this test we load a service worker in a page prior to starting the
+ * TargetCommand. We start the target list on another page, and then we go back to
+ * the first page. We want to check that we are correctly notified about the
+ * worker that was spawned before TargetCommand.
+ *
+ * Steps:
+ * - navigate to .com page
+ * - navigate to .org page
+ * - create target list
+ * - unregister .org worker
+ * - navigate back to .com page
+ * - unregister .com worker
+ *
+ * The expected calls are the same whether destroyServiceWorkersOnNavigation is
+ * true or false.
+ *
+ * Expected calls:
+ * - navigate to .com page
+ * - navigate to .org page
+ * - create target list
+ *   - onAvailable is called for the .org worker
+ * - unregister .org worker
+ *   - onDestroyed is called for the .org worker
+ * - navigate back to .com page
+ *   - onAvailable is called for the .com worker
+ * - unregister .com worker
+ *   - onDestroyed is called for the .com worker
+ */
+add_task(async function test_NavigationToPageWithExistingWorker_NoDestroy() {
+  await testNavigationToPageWithExistingWorker({
+    destroyServiceWorkersOnNavigation: false,
+  });
+});
+
+add_task(async function test_NavigationToPageWithExistingWorker_WithDestroy() {
+  await testNavigationToPageWithExistingWorker({
+    destroyServiceWorkersOnNavigation: true,
+  });
+});
+
+async function testNavigationToPageWithExistingWorker({
+  destroyServiceWorkersOnNavigation,
+}) {
+  await setupServiceWorkerNavigationTest();
+
+  const tab = await addTab(COM_PAGE_URL);
+
+  info("Wait until the service worker registration is registered");
+  await waitForRegistrationReady(tab, COM_PAGE_URL);
+
+  info("Navigate to another page");
+  let onBrowserLoaded = BrowserTestUtils.browserLoaded(
+    gBrowser.selectedBrowser
+  );
+  BrowserTestUtils.loadURIString(gBrowser.selectedBrowser, ORG_PAGE_URL);
+
+  // Avoid TV failures, where target list still starts thinking that the
+  // current domain is .com .
+  info("Wait until we have fully navigated to the .org page");
+  // wait for the browser to be loaded otherwise the task spawned in waitForRegistrationReady
+  // might be destroyed (when it still belongs to the previous content process)
+  await onBrowserLoaded;
+  await waitForRegistrationReady(tab, ORG_PAGE_URL);
+
+  const { hooks, commands, targetCommand } = await watchServiceWorkerTargets({
+    tab,
+    destroyServiceWorkersOnNavigation,
+  });
+
+  // We expect onAvailable to have been called one time, for the only service
+  // worker target available in the test page.
+  await checkHooks(hooks, {
+    available: 1,
+    destroyed: 0,
+    targets: [ORG_WORKER_URL],
+  });
+
+  info("Unregister .org service worker and wait until onDestroyed is called.");
+  await unregisterServiceWorker(tab, ORG_PAGE_URL);
+  await checkHooks(hooks, { available: 1, destroyed: 1, targets: [] });
+
+  info("Go back .com page, wait for onAvailable to be called");
+  onBrowserLoaded = BrowserTestUtils.browserLoaded(gBrowser.selectedBrowser);
+  BrowserTestUtils.loadURIString(gBrowser.selectedBrowser, COM_PAGE_URL);
+  await onBrowserLoaded;
+
+  await checkHooks(hooks, {
+    available: 2,
+    destroyed: 1,
+    targets: [COM_WORKER_URL],
+  });
+
+  info("Unregister .com service worker and wait until onDestroyed is called.");
+  await unregisterServiceWorker(tab, COM_PAGE_URL);
+  await checkHooks(hooks, { available: 2, destroyed: 2, targets: [] });
+
+  // Stop listening to avoid worker related requests
+  targetCommand.destroy();
+
+  await commands.waitForRequestsToSettle();
+  await commands.destroy();
+  await removeTab(tab);
+}
+
+async function setupServiceWorkerNavigationTest() {
+  // Disable the preloaded process as it creates processes intermittently
+  // which forces the emission of RDP requests we aren't correctly waiting for.
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+}
+
+async function watchServiceWorkerTargets({
+  destroyServiceWorkersOnNavigation,
+  tab,
+}) {
+  info("Create a target list for a tab target");
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+
+  // Enable Service Worker listening.
+  targetCommand.listenForServiceWorkers = true;
+  info(
+    "Set targetCommand.destroyServiceWorkersOnNavigation to " +
+      destroyServiceWorkersOnNavigation
+  );
+  targetCommand.destroyServiceWorkersOnNavigation =
+    destroyServiceWorkersOnNavigation;
+  await targetCommand.startListening();
+
+  // Setup onAvailable & onDestroyed callbacks so that we can check how many
+  // times they are called and with which targetFront.
+  const hooks = {
+    availableCount: 0,
+    destroyedCount: 0,
+    targets: [],
+  };
+
+  const onAvailable = async ({ targetFront }) => {
+    hooks.availableCount++;
+    hooks.targets.push(targetFront);
+  };
+
+  const onDestroyed = ({ targetFront }) => {
+    hooks.destroyedCount++;
+    hooks.targets.splice(hooks.targets.indexOf(targetFront), 1);
+  };
+
+  await targetCommand.watchTargets({
+    types: [targetCommand.TYPES.SERVICE_WORKER],
+    onAvailable,
+    onDestroyed,
+  });
+
+  return { hooks, commands, targetCommand };
+}
+
+async function unregisterServiceWorker(tab, expectedPageUrl) {
+  await waitForRegistrationReady(tab, expectedPageUrl);
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    // registrationPromise is set by the test page.
+    const registration = await content.wrappedJSObject.registrationPromise;
+    registration.unregister();
+  });
+}
+
+/**
+ * Wait until the expected URL is loaded and win.registration has resolved.
+ */
+async function waitForRegistrationReady(tab, expectedPageUrl) {
+  await asyncWaitUntil(() =>
+    SpecialPowers.spawn(tab.linkedBrowser, [expectedPageUrl], function (_url) {
+      try {
+        const win = content.wrappedJSObject;
+        const isExpectedUrl = win.location.href === _url;
+        const hasRegistration = !!win.registrationPromise;
+        return isExpectedUrl && hasRegistration;
+      } catch (e) {
+        return false;
+      }
+    })
+  );
+}
+
+/**
+ * Assert helper for the `hooks` object, updated by the onAvailable and
+ * onDestroyed callbacks. Assert that the callbacks have been called the
+ * expected number of times, with the expected targets.
+ */
+async function checkHooks(hooks, { available, destroyed, targets }) {
+  info(`Wait for availableCount=${available} and destroyedCount=${destroyed}`);
+  await waitUntil(
+    () => hooks.availableCount == available && hooks.destroyedCount == destroyed
+  );
+  is(hooks.availableCount, available, "onAvailable was called as expected");
+  is(hooks.destroyedCount, destroyed, "onDestroyed was called as expected");
+
+  is(hooks.targets.length, targets.length, "Expected number of targets");
+  targets.forEach((url, i) => {
+    is(hooks.targets[i].url, url, `SW target ${i} has the expected url`);
+  });
+}
diff --git a/devtools/shared/commands/target/tests/browser_target_command_switchToTarget.js b/devtools/shared/commands/target/tests/browser_target_command_switchToTarget.js
new file mode 100644
index 0000000000..04646117a9
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_switchToTarget.js
@@ -0,0 +1,138 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API switchToTarget function
+
+add_task(async function testSwitchToTarget() {
+  info("Test TargetCommand.switchToTarget method");
+
+  // Create a first target to switch from, a new tab with an iframe
+  const firstTab = await addTab(
+    `data:text/html,<iframe src="data:text/html,foo"></iframe>`
+  );
+  const commands = await CommandsFactory.forTab(firstTab);
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+  await targetCommand.startListening();
+
+  // Create a second target to switch to, a new tab with an iframe
+  const secondTab = await addTab(
+    `data:text/html,<iframe src="data:text/html,bar"></iframe>`
+  );
+  // We have to spawn a new distinct `commands` object for this new tab,
+  // but we will otherwise consider the first one as the main one.
+  // From this second one, we will only retrieve a new target.
+  const secondCommands = await CommandsFactory.forTab(secondTab, {
+    client: commands.client,
+  });
+  await secondCommands.targetCommand.startListening();
+  const secondTarget = secondCommands.targetCommand.targetFront;
+
+  const frameTargets = [];
+  const firstTarget = targetCommand.targetFront;
+  let currentTarget = targetCommand.targetFront;
+  const onFrameAvailable = ({ targetFront, isTargetSwitching }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "We are only notified about frame targets"
+    );
+    ok(
+      targetFront == currentTarget
+        ? targetFront.isTopLevel
+        : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
+    );
+    if (targetFront.isTopLevel) {
+      // When calling watchTargets, this will be false, but it will be true when calling switchToTarget
+      is(
+        isTargetSwitching,
+        currentTarget == secondTarget,
+        "target switching boolean is correct"
+      );
+    } else {
+      ok(!isTargetSwitching, "for now, only top level target can be switched");
+    }
+    frameTargets.push(targetFront);
+  };
+  const destroyedTargets = [];
+  const onFrameDestroyed = ({ targetFront, isTargetSwitching }) => {
+    is(
+      targetFront.targetType,
+      TYPES.FRAME,
+      "target-destroyed: We are only notified about frame targets"
+    );
+    ok(
+      targetFront == firstTarget
+        ? targetFront.isTopLevel
+        : !targetFront.isTopLevel,
+      "target-destroyed: isTopLevel property is correct"
+    );
+    if (targetFront.isTopLevel) {
+      is(
+        isTargetSwitching,
+        true,
+        "target-destroyed: target switching boolean is correct"
+      );
+    } else {
+      ok(
+        !isTargetSwitching,
+        "target-destroyed: for now, only top level target can be switched"
+      );
+    }
+    destroyedTargets.push(targetFront);
+  };
+  await targetCommand.watchTargets({
+    types: [TYPES.FRAME],
+    onAvailable: onFrameAvailable,
+    onDestroyed: onFrameDestroyed,
+  });
+
+  // Save the original list of targets
+  const createdTargets = [...frameTargets];
+  // Clear the recorded target list of all existing targets
+  frameTargets.length = 0;
+
+  currentTarget = secondTarget;
+  await targetCommand.switchToTarget(secondTarget);
+
+  is(
+    targetCommand.targetFront,
+    currentTarget,
+    "After the switch, the top level target has been updated"
+  );
+  // Because JS Window Actor API isn't used yet, FrameDescriptor.getTarget returns null
+  // And there is no target being created for the iframe, yet.
+  // As soon as bug 1565200 is resolved, this should return two frames, including the iframe.
+  is(
+    frameTargets.length,
+    1,
+    "We get the report of the top level iframe when switching to the new target"
+  );
+  is(frameTargets[0], currentTarget);
+  //is(frameTargets[1].url, "data:text/html,foo");
+
+  // Ensure that all the targets reported before the call to switchToTarget
+  // are reported as destroyed while calling switchToTarget.
+  is(
+    destroyedTargets.length,
+    createdTargets.length,
+    "All targets original reported are destroyed"
+  );
+  for (const newTarget of createdTargets) {
+    ok(
+      destroyedTargets.includes(newTarget),
+      "Each originally target is reported as destroyed"
+    );
+  }
+
+  targetCommand.destroy();
+
+  await commands.destroy();
+  await secondCommands.destroy();
+
+  BrowserTestUtils.removeTab(firstTab);
+  BrowserTestUtils.removeTab(secondTab);
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_tab_workers.js b/devtools/shared/commands/target/tests/browser_target_command_tab_workers.js
new file mode 100644
index 0000000000..24710879ae
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_tab_workers.js
@@ -0,0 +1,322 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API around workers
+
+const FISSION_TEST_URL = URL_ROOT_SSL + "fission_document.html";
+const IFRAME_FILE = "fission_iframe.html";
+const REMOTE_IFRAME_URL = URL_ROOT_ORG_SSL + IFRAME_FILE;
+const IFRAME_URL = URL_ROOT_SSL + IFRAME_FILE;
+const WORKER_FILE = "test_worker.js";
+const WORKER_URL = URL_ROOT_SSL + WORKER_FILE;
+const REMOTE_IFRAME_WORKER_URL = URL_ROOT_ORG_SSL + WORKER_FILE;
+
+add_task(async function () {
+  // Disable the preloaded process as it creates processes intermittently
+  // which forces the emission of RDP requests we aren't correctly waiting for.
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+
+  // The WorkerDebuggerManager#getWorkerDebuggerEnumerator method we're using to retrieve
+  // workers loops through _all_ the workers in the process, which means it goes over workers
+  // from other tabs as well. Here we add a few tabs that are not going to be used in the
+  // test, just to check that their workers won't be retrieved by getAllTargets/watchTargets.
+  await addTab(`${FISSION_TEST_URL}?id=first-untargetted-tab&noServiceWorker`);
+  await addTab(`${FISSION_TEST_URL}?id=second-untargetted-tab&noServiceWorker`);
+
+  info("Test TargetCommand against workers via a tab target");
+  const tab = await addTab(`${FISSION_TEST_URL}?&noServiceWorker`);
+
+  // Create a TargetCommand for the tab
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+
+  // Workaround to allow listening for workers in the content toolbox
+  // without the fission preferences
+  targetCommand.listenForWorkers = true;
+
+  await commands.targetCommand.startListening();
+
+  const { TYPES } = targetCommand;
+
+  info("Check that getAllTargets only returns dedicated workers");
+  const workers = await targetCommand.getAllTargets([
+    TYPES.WORKER,
+    TYPES.SHARED_WORKER,
+  ]);
+
+  // XXX: This should be modified in Bug 1607778, where we plan to add support for shared workers.
+  is(workers.length, 2, "Retrieved two worker…");
+  const mainPageWorker = workers.find(
+    worker => worker.url == `${WORKER_URL}#simple-worker`
+  );
+  const iframeWorker = workers.find(worker => {
+    return worker.url == `${REMOTE_IFRAME_WORKER_URL}#simple-worker-in-iframe`;
+  });
+  ok(mainPageWorker, "…the dedicated worker on the main page");
+  ok(iframeWorker, "…and the dedicated worker on the iframe");
+
+  info(
+    "Assert that watchTargets will call the create callback for existing dedicated workers"
+  );
+  const targets = [];
+  const destroyedTargets = [];
+  const onAvailable = async ({ targetFront }) => {
+    info(`onAvailable called for ${targetFront.url}`);
+    is(
+      targetFront.targetType,
+      TYPES.WORKER,
+      "We are only notified about worker targets"
+    );
+    ok(!targetFront.isTopLevel, "The workers are never top level");
+    targets.push(targetFront);
+    info(`Handled ${targets.length} targets\n`);
+  };
+  const onDestroyed = async ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.WORKER,
+      "We are only notified about worker targets"
+    );
+    ok(!targetFront.isTopLevel, "The workers are never top level");
+    destroyedTargets.push(targetFront);
+  };
+
+  await targetCommand.watchTargets({
+    types: [TYPES.WORKER, TYPES.SHARED_WORKER],
+    onAvailable,
+    onDestroyed,
+  });
+
+  // XXX: This should be modified in Bug 1607778, where we plan to add support for shared workers.
+  info("Check that watched targets return the same fronts as getAllTargets");
+  is(targets.length, 2, "watcheTargets retrieved 2 worker…");
+  const mainPageWorkerTarget = targets.find(t => t === mainPageWorker);
+  const iframeWorkerTarget = targets.find(t => t === iframeWorker);
+
+  ok(
+    mainPageWorkerTarget,
+    "…the dedicated worker in main page, which is the same front we received from getAllTargets"
+  );
+  ok(
+    iframeWorkerTarget,
+    "…the dedicated worker in iframe, which is the same front we received from getAllTargets"
+  );
+
+  info("Spawn workers in main page and iframe");
+  await SpecialPowers.spawn(tab.linkedBrowser, [WORKER_FILE], workerUrl => {
+    // Put the worker on the global so we can access it later
+    content.spawnedWorker = new content.Worker(`${workerUrl}#spawned-worker`);
+    const iframe = content.document.querySelector("iframe");
+    SpecialPowers.spawn(iframe, [workerUrl], innerWorkerUrl => {
+      // Put the worker on the global so we can access it later
+      content.spawnedWorker = new content.Worker(
+        `${innerWorkerUrl}#spawned-worker-in-iframe`
+      );
+    });
+  });
+
+  await waitFor(
+    () => targets.length === 4,
+    "Wait for the target list to notify us about the spawned worker"
+  );
+  const mainPageSpawnedWorkerTarget = targets.find(
+    innerTarget => innerTarget.url == `${WORKER_URL}#spawned-worker`
+  );
+  ok(mainPageSpawnedWorkerTarget, "Retrieved spawned worker");
+  const iframeSpawnedWorkerTarget = targets.find(
+    innerTarget =>
+      innerTarget.url == `${REMOTE_IFRAME_WORKER_URL}#spawned-worker-in-iframe`
+  );
+  ok(iframeSpawnedWorkerTarget, "Retrieved spawned worker in iframe");
+
+  await wait(100);
+
+  info(
+    "Check that the target list calls onDestroy when a worker is terminated"
+  );
+  await SpecialPowers.spawn(tab.linkedBrowser, [], () => {
+    content.spawnedWorker.terminate();
+    content.spawnedWorker = null;
+
+    SpecialPowers.spawn(content.document.querySelector("iframe"), [], () => {
+      content.spawnedWorker.terminate();
+      content.spawnedWorker = null;
+    });
+  });
+  await waitFor(
+    () =>
+      destroyedTargets.includes(mainPageSpawnedWorkerTarget) &&
+      destroyedTargets.includes(iframeSpawnedWorkerTarget),
+    "Wait for the target list to notify us about the terminated workers"
+  );
+
+  ok(
+    true,
+    "The target list handled the terminated workers (from the main page and the iframe)"
+  );
+
+  info(
+    "Check that reloading the page will notify about the terminated worker and the new existing one"
+  );
+  const targetsCountBeforeReload = targets.length;
+  await reloadBrowser();
+
+  await waitFor(() => {
+    return (
+      destroyedTargets.includes(mainPageWorkerTarget) &&
+      destroyedTargets.includes(iframeWorkerTarget)
+    );
+  }, `Wait for the target list to notify us about the terminated workers when reloading`);
+  ok(
+    true,
+    "The target list notified us about all the expected workers being destroyed when reloading"
+  );
+
+  await waitFor(
+    () => targets.length === targetsCountBeforeReload + 2,
+    "Wait for the target list to notify us about the new workers after reloading"
+  );
+
+  const mainPageWorkerTargetAfterReload = targets.find(
+    t => t !== mainPageWorkerTarget && t.url == `${WORKER_URL}#simple-worker`
+  );
+  const iframeWorkerTargetAfterReload = targets.find(
+    t =>
+      t !== iframeWorkerTarget &&
+      t.url == `${REMOTE_IFRAME_WORKER_URL}#simple-worker-in-iframe`
+  );
+
+  ok(
+    mainPageWorkerTargetAfterReload,
+    "The target list handled the worker created once the page navigated"
+  );
+  ok(
+    iframeWorkerTargetAfterReload,
+    "The target list handled the worker created in the iframe once the page navigated"
+  );
+
+  const targetCount = targets.length;
+
+  info(
+    "Check that when removing an iframe we're notified about its workers being terminated"
+  );
+  await SpecialPowers.spawn(tab.linkedBrowser, [], () => {
+    content.document.querySelector("iframe").remove();
+  });
+  await waitFor(() => {
+    return destroyedTargets.includes(iframeWorkerTargetAfterReload);
+  }, `Wait for the target list to notify us about the terminated workers when removing an iframe`);
+
+  info("Check that target list handles adding iframes with workers");
+  const iframeUrl = `${IFRAME_URL}?noServiceWorker=true&hashSuffix=in-created-iframe`;
+  const remoteIframeUrl = `${REMOTE_IFRAME_URL}?noServiceWorker=true&hashSuffix=in-created-remote-iframe`;
+
+  await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [iframeUrl, remoteIframeUrl],
+    (url, remoteUrl) => {
+      const firstIframe = content.document.createElement("iframe");
+      content.document.body.append(firstIframe);
+      firstIframe.src = url + "-1";
+
+      const secondIframe = content.document.createElement("iframe");
+      content.document.body.append(secondIframe);
+      secondIframe.src = url + "-2";
+
+      const firstRemoteIframe = content.document.createElement("iframe");
+      content.document.body.append(firstRemoteIframe);
+      firstRemoteIframe.src = remoteUrl + "-1";
+
+      const secondRemoteIframe = content.document.createElement("iframe");
+      content.document.body.append(secondRemoteIframe);
+      secondRemoteIframe.src = remoteUrl + "-2";
+    }
+  );
+
+  // It's important to check the length of `targets` here to ensure we don't get unwanted
+  // worker targets.
+  await waitFor(
+    () => targets.length === targetCount + 4,
+    "Wait for the target list to notify us about the workers in the new iframes"
+  );
+  const firstSpawnedIframeWorkerTarget = targets.find(
+    worker => worker.url == `${WORKER_URL}#simple-worker-in-created-iframe-1`
+  );
+  const secondSpawnedIframeWorkerTarget = targets.find(
+    worker => worker.url == `${WORKER_URL}#simple-worker-in-created-iframe-2`
+  );
+  const firstSpawnedRemoteIframeWorkerTarget = targets.find(
+    worker =>
+      worker.url ==
+      `${REMOTE_IFRAME_WORKER_URL}#simple-worker-in-created-remote-iframe-1`
+  );
+  const secondSpawnedRemoteIframeWorkerTarget = targets.find(
+    worker =>
+      worker.url ==
+      `${REMOTE_IFRAME_WORKER_URL}#simple-worker-in-created-remote-iframe-2`
+  );
+
+  ok(
+    firstSpawnedIframeWorkerTarget,
+    "The target list handled the worker in the first new same-origin iframe"
+  );
+  ok(
+    secondSpawnedIframeWorkerTarget,
+    "The target list handled the worker in the second new same-origin iframe"
+  );
+  ok(
+    firstSpawnedRemoteIframeWorkerTarget,
+    "The target list handled the worker in the first new remote iframe"
+  );
+  ok(
+    secondSpawnedRemoteIframeWorkerTarget,
+    "The target list handled the worker in the second new remote iframe"
+  );
+
+  info("Check that navigating away does destroy all targets");
+  BrowserTestUtils.loadURIString(
+    tab.linkedBrowser,
+    "data:text/html,<meta charset=utf8>Away"
+  );
+
+  await waitFor(
+    () => destroyedTargets.length === targets.length,
+    "Wait for all the targets to be reported as destroyed"
+  );
+
+  ok(
+    destroyedTargets.includes(mainPageWorkerTargetAfterReload),
+    "main page worker target was destroyed"
+  );
+  ok(
+    destroyedTargets.includes(firstSpawnedIframeWorkerTarget),
+    "first spawned same-origin iframe worker target was destroyed"
+  );
+  ok(
+    destroyedTargets.includes(secondSpawnedIframeWorkerTarget),
+    "second spawned same-origin iframe worker target was destroyed"
+  );
+  ok(
+    destroyedTargets.includes(firstSpawnedRemoteIframeWorkerTarget),
+    "first spawned remote iframe worker target was destroyed"
+  );
+  ok(
+    destroyedTargets.includes(secondSpawnedRemoteIframeWorkerTarget),
+    "second spawned remote iframe worker target was destroyed"
+  );
+
+  targetCommand.unwatchTargets({
+    types: [TYPES.WORKER, TYPES.SHARED_WORKER],
+    onAvailable,
+    onDestroyed,
+  });
+  targetCommand.destroy();
+
+  info("Unregister service workers so they don't appear in other tests.");
+  await unregisterAllServiceWorkers(commands.client);
+
+  BrowserTestUtils.removeTab(tab);
+  await commands.destroy();
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_tab_workers_bfcache_navigation.js b/devtools/shared/commands/target/tests/browser_target_command_tab_workers_bfcache_navigation.js
new file mode 100644
index 0000000000..0f1ea45a08
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_tab_workers_bfcache_navigation.js
@@ -0,0 +1,134 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test WORKER targets when doing history navigations (BF Cache)
+//
+// Use a distinct file as this test currently hits a DEBUG assertion
+// https://searchfox.org/mozilla-central/rev/352b525ab841278cd9b3098343f655ef85933544/dom/workers/WorkerPrivate.cpp#5218
+// and so is running only on OPT builds.
+
+const FISSION_TEST_URL = URL_ROOT_SSL + "fission_document.html";
+const WORKER_FILE = "test_worker.js";
+const WORKER_URL = URL_ROOT_SSL + WORKER_FILE;
+const IFRAME_WORKER_URL = URL_ROOT_ORG_SSL + WORKER_FILE;
+
+add_task(async function () {
+  // Disable the preloaded process as it creates processes intermittently
+  // which forces the emission of RDP requests we aren't correctly waiting for.
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+
+  // The WorkerDebuggerManager#getWorkerDebuggerEnumerator method we're using to retrieve
+  // workers loops through _all_ the workers in the process, which means it goes over workers
+  // from other tabs as well. Here we add a few tabs that are not going to be used in the
+  // test, just to check that their workers won't be retrieved by getAllTargets/watchTargets.
+  await addTab(`${FISSION_TEST_URL}?id=first-untargetted-tab&noServiceWorker`);
+  await addTab(`${FISSION_TEST_URL}?id=second-untargetted-tab&noServiceWorker`);
+
+  info("Test bfcache navigations");
+  const tab = await addTab(`${FISSION_TEST_URL}?&noServiceWorker`);
+
+  // Create a TargetCommand for the tab
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+
+  // Workaround to allow listening for workers in the content toolbox
+  // without the fission preferences
+  targetCommand.listenForWorkers = true;
+
+  await targetCommand.startListening();
+
+  const { TYPES } = targetCommand;
+
+  info(
+    "Assert that watchTargets will call the onAvailable callback for existing dedicated workers"
+  );
+  const targets = [];
+  const destroyedTargets = [];
+  const onAvailable = async ({ targetFront }) => {
+    info(`onAvailable called for ${targetFront.url}`);
+    is(
+      targetFront.targetType,
+      TYPES.WORKER,
+      "We are only notified about worker targets"
+    );
+    ok(!targetFront.isTopLevel, "The workers are never top level");
+    targets.push(targetFront);
+    info(`Handled ${targets.length} new targets`);
+  };
+  const onDestroyed = async ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.WORKER,
+      "We are only notified about worker targets"
+    );
+    ok(!targetFront.isTopLevel, "The workers are never top level");
+    destroyedTargets.push(targetFront);
+  };
+
+  await targetCommand.watchTargets({
+    types: [TYPES.WORKER, TYPES.SHARED_WORKER],
+    onAvailable,
+    onDestroyed,
+  });
+
+  is(targets.length, 2, "watchTargets retrieved 2 workers…");
+  const mainPageWorkerTarget = targets.find(
+    worker => worker.url == `${WORKER_URL}#simple-worker`
+  );
+  const iframeWorkerTarget = targets.find(
+    worker => worker.url == `${IFRAME_WORKER_URL}#simple-worker-in-iframe`
+  );
+
+  ok(
+    mainPageWorkerTarget,
+    "…the dedicated worker in main page, which is the same front we received from getAllTargets"
+  );
+  ok(
+    iframeWorkerTarget,
+    "…the dedicated worker in iframe, which is the same front we received from getAllTargets"
+  );
+
+  info("Check that navigating away does destroy all targets");
+  const onBrowserLoaded = BrowserTestUtils.browserLoaded(tab.linkedBrowser);
+  BrowserTestUtils.loadURIString(
+    tab.linkedBrowser,
+    "data:text/html,<meta charset=utf8>Away"
+  );
+  await onBrowserLoaded;
+
+  await waitFor(
+    () => destroyedTargets.length === 2,
+    "Wait for all the targets to be reported as destroyed"
+  );
+
+  info("Navigate back to the first page");
+  gBrowser.goBack();
+
+  await waitFor(
+    () => targets.length === 4,
+    "Wait for the target list to notify us about the first page workers, restored from the BF Cache"
+  );
+
+  const mainPageWorkerTargetAfterGoingBack = targets.find(
+    t => t !== mainPageWorkerTarget && t.url == `${WORKER_URL}#simple-worker`
+  );
+  const iframeWorkerTargetAfterGoingBack = targets.find(
+    t =>
+      t !== iframeWorkerTarget &&
+      t.url == `${IFRAME_WORKER_URL}#simple-worker-in-iframe`
+  );
+
+  ok(
+    mainPageWorkerTargetAfterGoingBack,
+    "The target list handled the worker created from the BF Cache"
+  );
+  ok(
+    iframeWorkerTargetAfterGoingBack,
+    "The target list handled the worker created in the iframe from the BF Cache"
+  );
+
+  targetCommand.destroy();
+  await commands.destroy();
+});
diff --git a/devtools/shared/commands/target/tests/browser_target_command_various_descriptors.js b/devtools/shared/commands/target/tests/browser_target_command_various_descriptors.js
new file mode 100644
index 0000000000..b61faf8f6e
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_various_descriptors.js
@@ -0,0 +1,283 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand API with all possible descriptors
+
+const TEST_URL = "https://example.org/document-builder.sjs?html=org";
+const SECOND_TEST_URL = "https://example.com/document-builder.sjs?html=org";
+const CHROME_WORKER_URL = CHROME_URL_ROOT + "test_worker.js";
+
+const DESCRIPTOR_TYPES = require("resource://devtools/client/fronts/descriptors/descriptor-types.js");
+
+add_task(async function () {
+  // Enabled fission prefs
+  await pushPref("devtools.browsertoolbox.scope", "everything");
+  // Disable the preloaded process as it gets created lazily and may interfere
+  // with process count assertions
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+  // This preference helps destroying the content process when we close the tab
+  await pushPref("dom.ipc.keepProcessesAlive.web", 1);
+
+  await testLocalTab();
+  await testRemoteTab();
+  await testParentProcess();
+  await testWorker();
+  await testWebExtension();
+});
+
+async function testParentProcess() {
+  info("Test TargetCommand against parent process descriptor");
+
+  const commands = await CommandsFactory.forMainProcess();
+  const { descriptorFront } = commands;
+
+  is(
+    descriptorFront.descriptorType,
+    DESCRIPTOR_TYPES.PROCESS,
+    "The descriptor type is correct"
+  );
+  is(
+    descriptorFront.isParentProcessDescriptor,
+    true,
+    "Descriptor front isParentProcessDescriptor is correct"
+  );
+  is(
+    descriptorFront.isProcessDescriptor,
+    true,
+    "Descriptor front isProcessDescriptor is correct"
+  );
+
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const targets = await targetCommand.getAllTargets(targetCommand.ALL_TYPES);
+  ok(
+    targets.length > 1,
+    "We get many targets when debugging the parent process"
+  );
+  const targetFront = targets[0];
+  is(targetFront, targetCommand.targetFront, "The first is the top level one");
+  is(
+    targetFront.targetType,
+    targetCommand.TYPES.FRAME,
+    "the parent process target is of frame type, because it inherits from WindowGlobalTargetActor"
+  );
+  is(targetFront.isTopLevel, true, "This is flagged as top level");
+
+  targetCommand.destroy();
+  await waitForAllTargetsToBeAttached(targetCommand);
+
+  await commands.destroy();
+}
+
+async function testLocalTab() {
+  info("Test TargetCommand against local tab descriptor (via getTab({ tab }))");
+
+  const tab = await addTab(TEST_URL);
+  const commands = await CommandsFactory.forTab(tab);
+  const { descriptorFront } = commands;
+  is(
+    descriptorFront.descriptorType,
+    DESCRIPTOR_TYPES.TAB,
+    "The descriptor type is correct"
+  );
+  is(
+    descriptorFront.isTabDescriptor,
+    true,
+    "Descriptor front isTabDescriptor is correct"
+  );
+
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const targets = await targetCommand.getAllTargets(targetCommand.ALL_TYPES);
+  is(targets.length, 1, "Got a unique target");
+  const targetFront = targets[0];
+  is(targetFront, targetCommand.targetFront, "The first is the top level one");
+  is(
+    targetFront.targetType,
+    targetCommand.TYPES.FRAME,
+    "the tab target is of frame type"
+  );
+  is(targetFront.isTopLevel, true, "This is flagged as top level");
+
+  targetCommand.destroy();
+
+  BrowserTestUtils.removeTab(tab);
+
+  await commands.destroy();
+}
+
+async function testRemoteTab() {
+  info(
+    "Test TargetCommand against remote tab descriptor (via getTab({ browserId }))"
+  );
+
+  const tab = await addTab(TEST_URL);
+  const commands = await CommandsFactory.forRemoteTab(
+    tab.linkedBrowser.browserId
+  );
+  const { descriptorFront } = commands;
+  is(
+    descriptorFront.descriptorType,
+    DESCRIPTOR_TYPES.TAB,
+    "The descriptor type is correct"
+  );
+  is(
+    descriptorFront.isTabDescriptor,
+    true,
+    "Descriptor front isTabDescriptor is correct"
+  );
+
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const targets = await targetCommand.getAllTargets(targetCommand.ALL_TYPES);
+  is(targets.length, 1, "Got a unique target");
+  const targetFront = targets[0];
+  is(
+    targetFront,
+    targetCommand.targetFront,
+    "TargetCommand top target is the same as the first target"
+  );
+  is(
+    targetFront.targetType,
+    targetCommand.TYPES.FRAME,
+    "the tab target is of frame type"
+  );
+  is(targetFront.isTopLevel, true, "This is flagged as top level");
+
+  const browser = tab.linkedBrowser;
+  const onLoaded = BrowserTestUtils.browserLoaded(browser);
+  await BrowserTestUtils.loadURIString(browser, SECOND_TEST_URL);
+  await onLoaded;
+
+  info("Wait for the new target");
+  await waitFor(() => targetCommand.targetFront != targetFront);
+  isnot(
+    targetCommand.targetFront,
+    targetFront,
+    "The top level target changes on navigation"
+  );
+  ok(
+    !targetCommand.targetFront.isDestroyed(),
+    "The new target isn't destroyed"
+  );
+  ok(targetFront.isDestroyed(), "While the previous target is destroyed");
+
+  targetCommand.destroy();
+
+  BrowserTestUtils.removeTab(tab);
+
+  await commands.destroy();
+}
+
+async function testWebExtension() {
+  info("Test TargetCommand against webextension descriptor");
+
+  const extension = ExtensionTestUtils.loadExtension({
+    useAddonManager: "temporary",
+    manifest: {
+      name: "Sample extension",
+    },
+  });
+
+  await extension.startup();
+
+  const commands = await CommandsFactory.forAddon(extension.id);
+  const { descriptorFront } = commands;
+  is(
+    descriptorFront.descriptorType,
+    DESCRIPTOR_TYPES.EXTENSION,
+    "The descriptor type is correct"
+  );
+  is(
+    descriptorFront.isWebExtensionDescriptor,
+    true,
+    "Descriptor front isWebExtensionDescriptor is correct"
+  );
+
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const targets = await targetCommand.getAllTargets(targetCommand.ALL_TYPES);
+  is(targets.length, 1, "Got a unique target");
+  const targetFront = targets[0];
+  is(targetFront, targetCommand.targetFront, "The first is the top level one");
+  is(
+    targetFront.targetType,
+    targetCommand.TYPES.FRAME,
+    "the web extension target is of frame type, because it inherits from WindowGlobalTargetActor"
+  );
+  is(targetFront.isTopLevel, true, "This is flagged as top level");
+
+  targetCommand.destroy();
+
+  await extension.unload();
+
+  await commands.destroy();
+}
+
+// CommandsFactory expect the worker id, which is computed from the nsIWorkerDebugger.id attribute
+function getNextWorkerDebuggerId() {
+  return new Promise(resolve => {
+    const wdm = Cc[
+      "@mozilla.org/dom/workers/workerdebuggermanager;1"
+    ].createInstance(Ci.nsIWorkerDebuggerManager);
+    const listener = {
+      onRegister(dbg) {
+        wdm.removeListener(listener);
+        resolve(dbg.id);
+      },
+    };
+    wdm.addListener(listener);
+  });
+}
+async function testWorker() {
+  info("Test TargetCommand against worker descriptor");
+
+  const workerUrl = CHROME_WORKER_URL + "#descriptor";
+  const onNextWorker = getNextWorkerDebuggerId();
+  const worker = new Worker(workerUrl);
+  const workerId = await onNextWorker;
+  ok(workerId, "Found the worker Debugger ID");
+
+  const commands = await CommandsFactory.forWorker(workerId);
+  const { descriptorFront } = commands;
+  is(
+    descriptorFront.descriptorType,
+    DESCRIPTOR_TYPES.WORKER,
+    "The descriptor type is correct"
+  );
+  is(
+    descriptorFront.isWorkerDescriptor,
+    true,
+    "Descriptor front isWorkerDescriptor is correct"
+  );
+
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const targets = await targetCommand.getAllTargets(targetCommand.ALL_TYPES);
+  is(targets.length, 1, "Got a unique target");
+  const targetFront = targets[0];
+  is(targetFront, targetCommand.targetFront, "The first is the top level one");
+  is(
+    targetFront.targetType,
+    targetCommand.TYPES.WORKER,
+    "the worker target is of worker type"
+  );
+  is(targetFront.isTopLevel, true, "This is flagged as top level");
+
+  targetCommand.destroy();
+
+  // Calling CommandsFactory.forWorker, will call RootFront.getWorker
+  // which will spawn lots of worker legacy code, firing lots of requests,
+  // which may still be pending
+  await commands.waitForRequestsToSettle();
+
+  await commands.destroy();
+  worker.terminate();
+}
diff --git a/devtools/shared/commands/target/tests/browser_target_command_watchTargets.js b/devtools/shared/commands/target/tests/browser_target_command_watchTargets.js
new file mode 100644
index 0000000000..516780be01
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_target_command_watchTargets.js
@@ -0,0 +1,214 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the TargetCommand's `watchTargets` function
+
+const TEST_URL =
+  "data:text/html;charset=utf-8," + encodeURIComponent(`<div id="test"></div>`);
+
+add_task(async function () {
+  // Enabled fission's pref as the TargetCommand is almost disabled without it
+  await pushPref("devtools.browsertoolbox.scope", "everything");
+  // Disable the preloaded process as it gets created lazily and may interfere
+  // with process count assertions
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+  // This preference helps destroying the content process when we close the tab
+  await pushPref("dom.ipc.keepProcessesAlive.web", 1);
+
+  await testWatchTargets();
+  await testThrowingInOnAvailable();
+});
+
+async function testWatchTargets() {
+  info("Test TargetCommand watchTargets function");
+
+  const commands = await CommandsFactory.forMainProcess();
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Note that ppmm also includes the parent process, which is considered as a frame rather than a process
+  const originalProcessesCount = Services.ppmm.childCount - 1;
+
+  info(
+    "Check that onAvailable is called for processes already created *before* the call to watchTargets"
+  );
+  const targets = new Set();
+  const topLevelTarget = targetCommand.targetFront;
+  const onAvailable = ({ targetFront }) => {
+    if (targets.has(targetFront)) {
+      ok(false, "The same target is notified multiple times via onAvailable");
+    }
+    is(
+      targetFront.targetType,
+      TYPES.PROCESS,
+      "We are only notified about process targets"
+    );
+    ok(
+      targetFront == topLevelTarget
+        ? targetFront.isTopLevel
+        : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
+    );
+    targets.add(targetFront);
+  };
+  const onDestroyed = ({ targetFront }) => {
+    if (!targets.has(targetFront)) {
+      ok(
+        false,
+        "A target is declared destroyed via onDestroyed without being notified via onAvailable"
+      );
+    }
+    is(
+      targetFront.targetType,
+      TYPES.PROCESS,
+      "We are only notified about process targets"
+    );
+    ok(
+      !targetFront.isTopLevel,
+      "We are not notified about the top level target destruction"
+    );
+    targets.delete(targetFront);
+  };
+  await targetCommand.watchTargets({
+    types: [TYPES.PROCESS],
+    onAvailable,
+    onDestroyed,
+  });
+  is(
+    targets.size,
+    originalProcessesCount,
+    "retrieved the expected number of processes via watchTargets"
+  );
+  // Start from 1 in order to ignore the parent process target, which is considered as a frame rather than a process
+  for (let i = 1; i < Services.ppmm.childCount; i++) {
+    const process = Services.ppmm.getChildAt(i);
+    const hasTargetWithSamePID = [...targets].find(
+      processTarget => processTarget.targetForm.processID == process.osPid
+    );
+    ok(
+      hasTargetWithSamePID,
+      `Process with PID ${process.osPid} has been reported via onAvailable`
+    );
+  }
+
+  info(
+    "Check that onAvailable is called for processes created *after* the call to watchTargets"
+  );
+  const previousTargets = new Set(targets);
+  const onProcessCreated = new Promise(resolve => {
+    const onAvailable2 = ({ targetFront }) => {
+      if (previousTargets.has(targetFront)) {
+        return;
+      }
+      targetCommand.unwatchTargets({
+        types: [TYPES.PROCESS],
+        onAvailable: onAvailable2,
+      });
+      resolve(targetFront);
+    };
+    targetCommand.watchTargets({
+      types: [TYPES.PROCESS],
+      onAvailable: onAvailable2,
+    });
+  });
+  const tab1 = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    url: TEST_URL,
+    forceNewProcess: true,
+  });
+  const createdTarget = await onProcessCreated;
+
+  // For some reason, creating a new tab purges processes created from previous tests
+  // so it is not reasonable to assert the side of `targets` as it may be lower than expected.
+  ok(targets.has(createdTarget), "The new tab process is in the list");
+
+  const processCountAfterTabOpen = targets.size;
+
+  // Assert that onDestroyed is called for destroyed processes
+  const onProcessDestroyed = new Promise(resolve => {
+    const onAvailable3 = () => {};
+    const onDestroyed3 = ({ targetFront }) => {
+      resolve(targetFront);
+      targetCommand.unwatchTargets({
+        types: [TYPES.PROCESS],
+        onAvailable: onAvailable3,
+        onDestroyed: onDestroyed3,
+      });
+    };
+    targetCommand.watchTargets({
+      types: [TYPES.PROCESS],
+      onAvailable: onAvailable3,
+      onDestroyed: onDestroyed3,
+    });
+  });
+
+  BrowserTestUtils.removeTab(tab1);
+
+  const destroyedTarget = await onProcessDestroyed;
+  is(
+    targets.size,
+    processCountAfterTabOpen - 1,
+    "The closed tab's process has been reported as destroyed"
+  );
+  ok(
+    !targets.has(destroyedTarget),
+    "The destroyed target is no longer in the list"
+  );
+  is(
+    destroyedTarget,
+    createdTarget,
+    "The destroyed target is the one that has been reported as created"
+  );
+
+  targetCommand.unwatchTargets({
+    types: [TYPES.PROCESS],
+    onAvailable,
+    onDestroyed,
+  });
+
+  targetCommand.destroy();
+
+  await commands.destroy();
+}
+
+async function testThrowingInOnAvailable() {
+  info(
+    "Test TargetCommand watchTargets function when an exception is thrown in onAvailable callback"
+  );
+
+  const commands = await CommandsFactory.forMainProcess();
+  const targetCommand = commands.targetCommand;
+  const { TYPES } = targetCommand;
+
+  await targetCommand.startListening();
+
+  // Note that ppmm also includes the parent process, which is considered as a frame rather than a process
+  const originalProcessesCount = Services.ppmm.childCount - 1;
+
+  info(
+    "Check that onAvailable is called for processes already created *before* the call to watchTargets"
+  );
+  const targets = new Set();
+  let thrown = false;
+  const onAvailable = ({ targetFront }) => {
+    if (!thrown) {
+      thrown = true;
+      throw new Error("Force an exception when processing the first target");
+    }
+    targets.add(targetFront);
+  };
+  await targetCommand.watchTargets({ types: [TYPES.PROCESS], onAvailable });
+  is(
+    targets.size,
+    originalProcessesCount - 1,
+    "retrieved the expected number of processes via onAvailable. All but the first one where we have thrown."
+  );
+
+  targetCommand.destroy();
+
+  await commands.destroy();
+}
diff --git a/devtools/shared/commands/target/tests/browser_watcher_actor_getter_caching.js b/devtools/shared/commands/target/tests/browser_watcher_actor_getter_caching.js
new file mode 100644
index 0000000000..6dd99d243b
--- /dev/null
+++ b/devtools/shared/commands/target/tests/browser_watcher_actor_getter_caching.js
@@ -0,0 +1,87 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that watcher front/actor APIs do not lead to create duplicate actors.
+
+const TEST_URL = "data:text/html;charset=utf-8,Actor caching test";
+
+add_task(async function () {
+  info("Setup the test page with workers of all types");
+  const tab = await addTab(TEST_URL);
+
+  info("Create a target list for a tab target");
+  const commands = await CommandsFactory.forTab(tab);
+  const targetCommand = commands.targetCommand;
+  await targetCommand.startListening();
+
+  const { watcherFront } = targetCommand;
+  ok(watcherFront, "A watcherFront is available on targetCommand");
+
+  info("Check that getNetworkParentActor does not create duplicate actors");
+  testActorGetter(
+    watcherFront,
+    () => watcherFront.getNetworkParentActor(),
+    "networkParent"
+  );
+
+  info("Check that getBreakpointListActor does not create duplicate actors");
+  testActorGetter(
+    watcherFront,
+    () => watcherFront.getBreakpointListActor(),
+    "breakpoint-list"
+  );
+
+  info(
+    "Check that getTargetConfigurationActor does not create duplicate actors"
+  );
+  testActorGetter(
+    watcherFront,
+    () => watcherFront.getTargetConfigurationActor(),
+    "target-configuration"
+  );
+
+  info(
+    "Check that getThreadConfigurationActor does not create duplicate actors"
+  );
+  testActorGetter(
+    watcherFront,
+    () => watcherFront.getThreadConfigurationActor(),
+    "thread-configuration"
+  );
+
+  targetCommand.destroy();
+  await commands.waitForRequestsToSettle();
+  await commands.destroy();
+});
+
+/**
+ * Check that calling an actor getter method on the watcher front leads to the
+ * creation of at most 1 actor.
+ */
+async function testActorGetter(watcherFront, actorGetterFn, typeName) {
+  checkPoolChildrenSize(watcherFront, typeName, 0);
+
+  const actor = await actorGetterFn();
+  checkPoolChildrenSize(watcherFront, typeName, 1);
+
+  const otherActor = await actorGetterFn();
+  is(actor, otherActor, "Returned the same actor for " + typeName);
+
+  checkPoolChildrenSize(watcherFront, typeName, 1);
+}
+
+/**
+ * Assert that a given parent pool has the expected number of children for
+ * a given typeName.
+ */
+function checkPoolChildrenSize(parentPool, typeName, expected) {
+  const children = [...parentPool.poolChildren()];
+  const childrenByType = children.filter(pool => pool.typeName === typeName);
+  is(
+    childrenByType.length,
+    expected,
+    `${parentPool.actorID} should have ${expected} children of type ${typeName}`
+  );
+}
diff --git a/devtools/shared/commands/target/tests/fission_document.html b/devtools/shared/commands/target/tests/fission_document.html
new file mode 100644
index 0000000000..62afe347e3
--- /dev/null
+++ b/devtools/shared/commands/target/tests/fission_document.html
@@ -0,0 +1,47 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf8">
+  <title>Test fission document</title>
+  <!-- Any copyright is dedicated to the Public Domain.
+     - http://creativecommons.org/publicdomain/zero/1.0/ -->
+  <script>
+  "use strict";
+
+  const params = new URLSearchParams(document.location.search);
+
+  // eslint-disable-next-line no-unused-vars
+  const worker = new Worker("https://example.com/browser/devtools/shared/commands/target/tests/test_worker.js#simple-worker");
+
+  // eslint-disable-next-line no-unused-vars
+  const sharedWorker = new SharedWorker("https://example.com/browser/devtools/shared/commands/target/tests/test_worker.js#shared-worker");
+
+  if (!params.has("noServiceWorker")) {
+    // Expose a reference to the registration so that tests can unregister it.
+    window.registrationPromise = navigator.serviceWorker.register("https://example.com/browser/devtools/shared/commands/target/tests/test_service_worker.js#service-worker");
+  }
+
+  /* exported logMessageInWorker */
+  function logMessageInWorker(message) {
+    worker.postMessage({
+      type: "log-in-worker",
+      message,
+    });
+  }
+  </script>
+</head>
+<body>
+<p>Test fission iframe</p>
+
+<script>
+  "use strict";
+  const iframe = document.createElement("iframe");
+  let iframeUrl = `https://example.org/browser/devtools/shared/commands/target/tests/fission_iframe.html`;
+  if (document.location.search) {
+    iframeUrl += `?${new URLSearchParams(document.location.search)}`;
+  }
+  iframe.src = iframeUrl;
+  document.body.append(iframe);
+</script>
+</body>
+</html>
diff --git a/devtools/shared/commands/target/tests/fission_iframe.html b/devtools/shared/commands/target/tests/fission_iframe.html
new file mode 100644
index 0000000000..deae49f833
--- /dev/null
+++ b/devtools/shared/commands/target/tests/fission_iframe.html
@@ -0,0 +1,29 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf8">
+  <title>Test fission iframe document</title>
+  <!-- Any copyright is dedicated to the Public Domain.
+     - http://creativecommons.org/publicdomain/zero/1.0/ -->
+  <script>
+    "use strict";
+    const params = new URLSearchParams(document.location.search);
+    const hashSuffix = params.get("hashSuffix") || "in-iframe";
+    // eslint-disable-next-line no-unused-vars
+    const worker = new Worker("test_worker.js#simple-worker-" + hashSuffix);
+    // eslint-disable-next-line no-unused-vars
+    const sharedWorker = new SharedWorker("test_worker.js#shared-worker-" + hashSuffix);
+
+    /* exported logMessageInWorker */
+    function logMessageInWorker(message) {
+      worker.postMessage({
+        type: "log-in-worker",
+        message,
+      });
+    }
+  </script>
+</head>
+<body>
+<p>remote iframe</p>
+</body>
+</html>
diff --git a/devtools/shared/commands/target/tests/head.js b/devtools/shared/commands/target/tests/head.js
new file mode 100644
index 0000000000..ecb3fc1828
--- /dev/null
+++ b/devtools/shared/commands/target/tests/head.js
@@ -0,0 +1,32 @@
+/* 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/. */
+
+"use strict";
+
+/* eslint no-unused-vars: [2, {"vars": "local"}] */
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/devtools/client/shared/test/shared-head.js",
+  this
+);
+
+const {
+  DevToolsClient,
+} = require("resource://devtools/client/devtools-client.js");
+const {
+  DevToolsServer,
+} = require("resource://devtools/server/devtools-server.js");
+
+async function createLocalClient() {
+  // Instantiate a minimal server
+  DevToolsServer.init();
+  DevToolsServer.allowChromeProcess = true;
+  if (!DevToolsServer.createRootActor) {
+    DevToolsServer.registerAllActors();
+  }
+  const transport = DevToolsServer.connectPipe();
+  const client = new DevToolsClient(transport);
+  await client.connect();
+  return client;
+}
diff --git a/devtools/shared/commands/target/tests/incremental-js-value-script.sjs b/devtools/shared/commands/target/tests/incremental-js-value-script.sjs
new file mode 100644
index 0000000000..a612a3cb59
--- /dev/null
+++ b/devtools/shared/commands/target/tests/incremental-js-value-script.sjs
@@ -0,0 +1,23 @@
+"use strict";
+
+function handleRequest(request, response) {
+  const Etag = '"4d881ab-b03-435f0a0f9ef00"';
+  const IfNoneMatch = request.hasHeader("If-None-Match")
+    ? request.getHeader("If-None-Match")
+    : "";
+
+  const counter = getState("cache-counter") || 1;
+  const page = "<script>var jsValue = '" + counter + "';</script>" + counter;
+
+  setState("cache-counter", "" + (parseInt(counter, 10) + 1));
+
+  response.setHeader("Etag", Etag, false);
+
+  if (IfNoneMatch === Etag) {
+    response.setStatusLine(request.httpVersion, "304", "Not Modified");
+  } else {
+    response.setHeader("Content-Type", "text/html; charset=utf-8", false);
+    response.setHeader("Content-Length", page.length + "", false);
+    response.write(page);
+  }
+}
diff --git a/devtools/shared/commands/target/tests/simple_document.html b/devtools/shared/commands/target/tests/simple_document.html
new file mode 100644
index 0000000000..d6a449e489
--- /dev/null
+++ b/devtools/shared/commands/target/tests/simple_document.html
@@ -0,0 +1,12 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf8">
+  <title>Test empty document</title>
+  <!-- Any copyright is dedicated to the Public Domain.
+     - http://creativecommons.org/publicdomain/zero/1.0/ -->
+</head>
+<body>
+<p>Test empty document</p>
+</body>
+</html>
diff --git a/devtools/shared/commands/target/tests/test_service_worker.js b/devtools/shared/commands/target/tests/test_service_worker.js
new file mode 100644
index 0000000000..aabc3fda0f
--- /dev/null
+++ b/devtools/shared/commands/target/tests/test_service_worker.js
@@ -0,0 +1,11 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// We don't need any computation in the worker,
+// but at least register a fetch listener so that
+// we force instantiating the SW when loading the page.
+self.onfetch = function (event) {
+  // do nothing.
+};
diff --git a/devtools/shared/commands/target/tests/test_sw_page.html b/devtools/shared/commands/target/tests/test_sw_page.html
new file mode 100644
index 0000000000..38aad04259
--- /dev/null
+++ b/devtools/shared/commands/target/tests/test_sw_page.html
@@ -0,0 +1,19 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf8">
+  <title>Test sw page</title>
+  <!-- Any copyright is dedicated to the Public Domain.
+     - http://creativecommons.org/publicdomain/zero/1.0/ -->
+</head>
+<body>
+<p>Test sw page</p>
+
+<script>
+"use strict";
+
+// Expose a reference to the registration so that tests can unregister it.
+window.registrationPromise = navigator.serviceWorker.register("test_sw_page_worker.js");
+</script>
+</body>
+</html>
diff --git a/devtools/shared/commands/target/tests/test_sw_page_worker.js b/devtools/shared/commands/target/tests/test_sw_page_worker.js
new file mode 100644
index 0000000000..29cda68560
--- /dev/null
+++ b/devtools/shared/commands/target/tests/test_sw_page_worker.js
@@ -0,0 +1,5 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// We don't need any computation in the worker,
+// just it to be alive
diff --git a/devtools/shared/commands/target/tests/test_worker.js b/devtools/shared/commands/target/tests/test_worker.js
new file mode 100644
index 0000000000..ce3dd39cea
--- /dev/null
+++ b/devtools/shared/commands/target/tests/test_worker.js
@@ -0,0 +1,13 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+globalThis.onmessage = function (e) {
+  const { type, message } = e.data;
+
+  if (type === "log-in-worker") {
+    // Printing `e` so we can check that we have an object and not a stringified version
+    console.log("[WORKER]", message, e);
+  }
+};