diff --git a/devtools/client/accessibility/accessibility-proxy.js b/devtools/client/accessibility/accessibility-proxy.js
index 120b354140c6..1bb5b90df28d 100644
--- a/devtools/client/accessibility/accessibility-proxy.js
+++ b/devtools/client/accessibility/accessibility-proxy.js
@@ -307,8 +307,8 @@ class AccessibilityProxy {
       : this.accessibilityEventsMap;
   }
 
-  async _onTargetAvailable({ targetFront, isTopLevel }) {
-    if (isTopLevel) {
+  async _onTargetAvailable({ targetFront }) {
+    if (targetFront.isTopLevel) {
       await this._updateTarget(targetFront);
     }
   }
diff --git a/devtools/client/accessibility/panel.js b/devtools/client/accessibility/panel.js
index 419be7217473..f246f1c2c542 100644
--- a/devtools/client/accessibility/panel.js
+++ b/devtools/client/accessibility/panel.js
@@ -162,8 +162,8 @@ AccessibilityPanel.prototype = {
     this._opening.then(() => this.refresh());
   },
 
-  async onTargetAvailable({ targetFront, isTopLevel, isTargetSwitching }) {
-    if (isTopLevel) {
+  async onTargetAvailable({ targetFront, isTargetSwitching }) {
+    if (targetFront.isTopLevel) {
       await this.accessibilityProxy.initializeProxyForPanel(targetFront);
       this.accessibilityProxy.currentTarget.on("navigate", this.onTabNavigated);
     }
diff --git a/devtools/client/application/initializer.js b/devtools/client/application/initializer.js
index c08290f26d87..ec1e71acfabf 100644
--- a/devtools/client/application/initializer.js
+++ b/devtools/client/application/initializer.js
@@ -126,16 +126,16 @@ window.Application = {
     targetFront.off("navigate", this.handleOnNavigate);
   },
 
-  onTargetAvailable({ targetFront, isTopLevel }) {
-    if (!isTopLevel) {
+  onTargetAvailable({ targetFront }) {
+    if (!targetFront.isTopLevel) {
       return; // ignore target frames that are not top level for now
     }
 
     this.setupTarget(targetFront);
   },
 
-  onTargetDestroyed({ targetFront, isTopLevel }) {
-    if (!isTopLevel) {
+  onTargetDestroyed({ targetFront }) {
+    if (!targetFront.isTopLevel) {
       return; // ignore target frames that are not top level for now
     }
 
diff --git a/devtools/client/debugger/src/client/firefox.js b/devtools/client/debugger/src/client/firefox.js
index 3661391beb22..37e8f3e81c22 100644
--- a/devtools/client/debugger/src/client/firefox.js
+++ b/devtools/client/debugger/src/client/firefox.js
@@ -33,10 +33,9 @@ export async function onConnect(
 
 async function onTargetAvailable({
   targetFront,
-  isTopLevel,
   isTargetSwitching,
 }): Promise<void> {
-  if (!isTopLevel) {
+  if (!targetFront.isTopLevel) {
     return;
   }
 
@@ -91,8 +90,8 @@ async function onTargetAvailable({
   await clientCommands.checkIfAlreadyPaused();
 }
 
-function onTargetDestroyed({ targetFront, isTopLevel }): void {
-  if (isTopLevel) {
+function onTargetDestroyed({ targetFront }): void {
+  if (targetFront.isTopLevel) {
     targetFront.off("will-navigate", actions.willNavigate);
     targetFront.off("navigate", actions.navigated);
     removeEventsTopTarget(targetFront);
diff --git a/devtools/client/dom/panel.js b/devtools/client/dom/panel.js
index 3602158f011b..a6110748a5a8 100644
--- a/devtools/client/dom/panel.js
+++ b/devtools/client/dom/panel.js
@@ -130,9 +130,9 @@ DomPanel.prototype = {
     this.refresh();
   },
 
-  onTargetAvailable: function({ isTopLevel, isTargetSwitching }) {
+  onTargetAvailable: function({ targetFront }) {
     // Only care about top-level targets.
-    if (!isTopLevel) {
+    if (!targetFront.isTopLevel) {
       return;
     }
 
diff --git a/devtools/client/framework/toolbox.js b/devtools/client/framework/toolbox.js
index 704f281d1273..159df69ca53c 100644
--- a/devtools/client/framework/toolbox.js
+++ b/devtools/client/framework/toolbox.js
@@ -722,8 +722,8 @@ Toolbox.prototype = {
    * This method will be called for the top-level target, as well as any potential
    * additional targets we may care about.
    */
-  async _onTargetAvailable({ type, targetFront, isTopLevel }) {
-    if (isTopLevel) {
+  async _onTargetAvailable({ targetFront }) {
+    if (targetFront.isTopLevel) {
       // Attach to a new top-level target.
       // For now, register these event listeners only on the top level target
       targetFront.on("will-navigate", this._onWillNavigate);
@@ -736,19 +736,19 @@ Toolbox.prototype = {
       });
     }
 
-    await this._attachTarget({ type, targetFront, isTopLevel });
+    await this._attachTarget(targetFront);
 
     if (this.hostType !== Toolbox.HostType.PAGE) {
       await this.store.dispatch(registerTarget(targetFront));
     }
 
-    if (isTopLevel) {
+    if (targetFront.isTopLevel) {
       this.emit("top-target-attached");
     }
   },
 
-  _onTargetDestroyed({ type, targetFront, isTopLevel }) {
-    if (isTopLevel) {
+  _onTargetDestroyed({ targetFront }) {
+    if (targetFront.isTopLevel) {
       this.detachTarget();
     }
 
@@ -764,7 +764,7 @@ Toolbox.prototype = {
    * And we listen for thread actor events in order to update toolbox UI when
    * we hit a breakpoint.
    */
-  async _attachTarget({ type, targetFront, isTopLevel }) {
+  async _attachTarget(targetFront) {
     await targetFront.attach();
 
     // Start tracking network activity on toolbox open for targets such as tabs.
@@ -775,10 +775,13 @@ Toolbox.prototype = {
     // already tracked by the content process targets. At least in the context
     // of the Browser Toolbox.
     // We would have to revisit that for the content toolboxes.
-    if (isTopLevel || type != TargetList.TYPES.FRAME) {
+    if (
+      targetFront.isTopLevel ||
+      targetFront.targetType != TargetList.TYPES.FRAME
+    ) {
       const threadFront = await this._attachAndResumeThread(targetFront);
       this._startThreadFrontListeners(threadFront);
-      if (isTopLevel) {
+      if (targetFront.isTopLevel) {
         this._threadFront = threadFront;
       }
     }
diff --git a/devtools/client/inspector/animation/animation.js b/devtools/client/inspector/animation/animation.js
index 2f271b5fa093..4bb6b8288f42 100644
--- a/devtools/client/inspector/animation/animation.js
+++ b/devtools/client/inspector/animation/animation.js
@@ -445,8 +445,8 @@ class AnimationInspector {
     this.inspector.store.dispatch(updateSidebarSize(size));
   }
 
-  async onTargetAvailable({ isTopLevel, targetFront }) {
-    if (isTopLevel) {
+  async onTargetAvailable({ targetFront }) {
+    if (targetFront.isTopLevel) {
       this.animationsFront = await targetFront.getFront("animations");
       this.animationsFront.setWalkerActor(this.inspector.walker);
       this.animationsFront.on("mutations", this.onAnimationsMutation);
diff --git a/devtools/client/inspector/changes/ChangesView.js b/devtools/client/inspector/changes/ChangesView.js
index 28333cf40a48..2e4419c98665 100644
--- a/devtools/client/inspector/changes/ChangesView.js
+++ b/devtools/client/inspector/changes/ChangesView.js
@@ -126,26 +126,26 @@ class ChangesView {
     changesFront.off("clear-changes", this.onClearChanges);
   }
 
-  async onTargetAvailable({ type, targetFront, isTopLevel }) {
+  async onTargetAvailable({ targetFront }) {
     targetFront.watchFronts(
       "changes",
       this.onChangesFrontAvailable,
       this.onChangesFrontDestroyed
     );
 
-    if (isTopLevel) {
+    if (targetFront.isTopLevel) {
       targetFront.on("will-navigate", this.onClearChanges);
     }
   }
 
-  async onTargetDestroyed({ type, targetFront, isTopLevel }) {
+  async onTargetDestroyed({ targetFront }) {
     targetFront.unwatchFronts(
       "changes",
       this.onChangesFrontAvailable,
       this.onChangesFrontDestroyed
     );
 
-    if (isTopLevel) {
+    if (targetFront.isTopLevel) {
       targetFront.off("will-navigate", this.onClearChanges);
     }
   }
diff --git a/devtools/client/inspector/inspector.js b/devtools/client/inspector/inspector.js
index b0c4016c7e93..ff01249c7d44 100644
--- a/devtools/client/inspector/inspector.js
+++ b/devtools/client/inspector/inspector.js
@@ -213,9 +213,9 @@ Inspector.prototype = {
     return this._deferredOpen();
   },
 
-  async _onTargetAvailable({ type, targetFront, isTopLevel }) {
+  async _onTargetAvailable({ targetFront }) {
     // Ignore all targets but the top level one
-    if (!isTopLevel) {
+    if (!targetFront.isTopLevel) {
       return;
     }
 
@@ -229,9 +229,9 @@ Inspector.prototype = {
     ]);
   },
 
-  _onTargetDestroyed({ type, targetFront, isTopLevel }) {
+  _onTargetDestroyed({ targetFront }) {
     // Ignore all targets but the top level one
-    if (!isTopLevel) {
+    if (!targetFront.isTopLevel) {
       return;
     }
     targetFront.off("will-navigate", this._onBeforeNavigate);
diff --git a/devtools/client/inspector/shared/walker-event-listener.js b/devtools/client/inspector/shared/walker-event-listener.js
index 2ebdf1c7ecc1..ac493176b342 100644
--- a/devtools/client/inspector/shared/walker-event-listener.js
+++ b/devtools/client/inspector/shared/walker-event-listener.js
@@ -59,7 +59,7 @@ class WalkerEventListener {
     );
   }
 
-  async _onTargetAvailable({ type, targetFront, isTopLevel }) {
+  async _onTargetAvailable({ targetFront }) {
     const inspectorFront = await targetFront.getFront("inspector");
     const { walker } = inspectorFront;
     for (const [name, listener] of Object.entries(this._listenerMap)) {
@@ -67,7 +67,7 @@ class WalkerEventListener {
     }
   }
 
-  _onTargetDestroyed({ type, targetFront, isTopLevel }) {
+  _onTargetDestroyed({ targetFront }) {
     const inspectorFront = targetFront.getCachedFront("inspector");
     if (inspectorFront) {
       const { walker } = inspectorFront;
diff --git a/devtools/client/memory/panel.js b/devtools/client/memory/panel.js
index 7e600723a098..71728b300533 100644
--- a/devtools/client/memory/panel.js
+++ b/devtools/client/memory/panel.js
@@ -44,8 +44,8 @@ MemoryPanel.prototype = {
     return this;
   },
 
-  async _onTargetAvailable({ targetFront, isTopLevel }) {
-    if (isTopLevel) {
+  async _onTargetAvailable({ targetFront }) {
+    if (targetFront.isTopLevel) {
       const front = await targetFront.getFront("memory");
       await front.attach();
       this.initializer.updateFront(front);
diff --git a/devtools/client/netmonitor/src/connector/firefox-connector.js b/devtools/client/netmonitor/src/connector/firefox-connector.js
index a8e23c5aa171..b88b359f29eb 100644
--- a/devtools/client/netmonitor/src/connector/firefox-connector.js
+++ b/devtools/client/netmonitor/src/connector/firefox-connector.js
@@ -117,8 +117,8 @@ class FirefoxConnector {
     await this.addListeners();
   }
 
-  async onTargetAvailable({ targetFront, isTopLevel, isTargetSwitching }) {
-    if (!isTopLevel) {
+  async onTargetAvailable({ targetFront, isTargetSwitching }) {
+    if (!targetFront.isTopLevel) {
       return;
     }
 
diff --git a/devtools/client/performance/panel.js b/devtools/client/performance/panel.js
index 066f5bb04f04..b8e5ca45bf9e 100644
--- a/devtools/client/performance/panel.js
+++ b/devtools/client/performance/panel.js
@@ -116,11 +116,9 @@ PerformancePanel.prototype = {
    * @param {TargetFront} - targetFront
    *        As we are watching only FRAME type for this panel,
    *        the target should be a instance of BrowsingContextTarget.
-   * @param {Boolean} - isTopLevel
-   *        true if the target is a full page.
    */
-  async _handleTargetAvailable({ targetFront, isTopLevel }) {
-    if (isTopLevel) {
+  async _handleTargetAvailable({ targetFront }) {
+    if (targetFront.isTopLevel) {
       const { PerformanceController, PerformanceView } = this.panelWin;
       const performanceFront = await targetFront.getFront("performance");
 
diff --git a/devtools/client/responsive/ui.js b/devtools/client/responsive/ui.js
index b07d6a7a98b2..bd9db4e2250c 100644
--- a/devtools/client/responsive/ui.js
+++ b/devtools/client/responsive/ui.js
@@ -1177,8 +1177,8 @@ class ResponsiveUI {
     return this.browserWindow;
   }
 
-  async onTargetAvailable({ isTopLevel, targetFront }) {
-    if (isTopLevel) {
+  async onTargetAvailable({ targetFront }) {
+    if (targetFront.isTopLevel) {
       this.responsiveFront = await targetFront.getFront("responsive");
       await this.restoreActorState();
     }
diff --git a/devtools/client/storage/ui.js b/devtools/client/storage/ui.js
index 588ec5af3063..eff005a5fa5f 100644
--- a/devtools/client/storage/ui.js
+++ b/devtools/client/storage/ui.js
@@ -279,10 +279,10 @@ class StorageUI {
     );
   }
 
-  async _onTargetAvailable({ type, targetFront, isTopLevel }) {
+  async _onTargetAvailable({ targetFront }) {
     // Only support top level target and navigation to new processes.
     // i.e. ignore additional targets created for remote <iframes>
-    if (!isTopLevel) {
+    if (!targetFront.isTopLevel) {
       return;
     }
 
@@ -324,10 +324,10 @@ class StorageUI {
     }
   }
 
-  _onTargetDestroyed({ type, targetFront, isTopLevel }) {
+  _onTargetDestroyed({ targetFront }) {
     // Only support top level target and navigation to new processes.
     // i.e. ignore additional targets created for remote <iframes>
-    if (!isTopLevel) {
+    if (!targetFront.isTopLevel) {
       return;
     }
 
diff --git a/devtools/client/styleeditor/StyleEditorUI.jsm b/devtools/client/styleeditor/StyleEditorUI.jsm
index f3b05fb0a73c..639c64a21b88 100644
--- a/devtools/client/styleeditor/StyleEditorUI.jsm
+++ b/devtools/client/styleeditor/StyleEditorUI.jsm
@@ -1133,8 +1133,8 @@ StyleEditorUI.prototype = {
     this.selectStyleSheet(source, location.line - 1, location.column - 1);
   },
 
-  async _onTargetAvailable({ targetFront, isTopLevel }) {
-    if (isTopLevel) {
+  async _onTargetAvailable({ targetFront }) {
+    if (targetFront.isTopLevel) {
       await this.initializeHighlighter(targetFront);
 
       const stylesheetsFront = await targetFront.getFront("stylesheets");
@@ -1146,8 +1146,8 @@ StyleEditorUI.prototype = {
     }
   },
 
-  async _onTargetDestroyed({ isTopLevel }) {
-    if (isTopLevel) {
+  async _onTargetDestroyed({ targetFront }) {
+    if (targetFront.isTopLevel) {
       this._clear();
     }
   },
diff --git a/devtools/client/webconsole/webconsole-ui.js b/devtools/client/webconsole/webconsole-ui.js
index 88af3d264ffe..98203d50c851 100644
--- a/devtools/client/webconsole/webconsole-ui.js
+++ b/devtools/client/webconsole/webconsole-ui.js
@@ -373,34 +373,25 @@ class WebConsoleUI {
    * i.e. it was already existing or has just been created.
    *
    * @private
-   * @param string type
-   *        One of the string of TargetList.TYPES to describe which
-   *        type of target is available.
    * @param Front targetFront
    *        The Front of the target that is available.
    *        This Front inherits from TargetMixin and is typically
    *        composed of a BrowsingContextTargetFront or ContentProcessTargetFront.
-   * @param boolean isTopLevel
-   *        If true, means that this is the top level target.
-   *        This typically happens on startup, providing the current
-   *        top level target. But also on navigation, when we navigate
-   *        to an URL which has to be loaded in a distinct process.
-   *        A new top level target is created.
    */
-  async _onTargetAvailable({ type, targetFront, isTopLevel }) {
+  async _onTargetAvailable({ targetFront }) {
     const dispatchTargetAvailable = () => {
       const store = this.wrapper && this.wrapper.getStore();
       if (store) {
         this.wrapper.getStore().dispatch({
           type: constants.TARGET_AVAILABLE,
-          targetType: type,
+          targetType: targetFront.targetType,
         });
       }
     };
 
     // This is a top level target. It may update on process switches
     // when navigating to another domain.
-    if (isTopLevel) {
+    if (targetFront.isTopLevel) {
       const fissionSupport = Services.prefs.getBoolPref(
         constants.PREFS.FEATURES.BROWSER_TOOLBOX_FISSION
       );
@@ -425,8 +416,9 @@ class WebConsoleUI {
       isContentToolbox &&
       Services.prefs.getBoolPref("devtools.contenttoolbox.fission");
     if (
-      type != this.hud.targetList.TYPES.PROCESS &&
-      (type != this.hud.targetList.TYPES.FRAME || !listenForFrames)
+      targetFront.targetType != this.hud.targetList.TYPES.PROCESS &&
+      (targetFront.targetType != this.hud.targetList.TYPES.FRAME ||
+        !listenForFrames)
     ) {
       return;
     }
@@ -442,8 +434,8 @@ class WebConsoleUI {
    * @private
    * See _onTargetAvailable for param's description.
    */
-  _onTargetDestroyed({ type, targetFront, isTopLevel }) {
-    if (isTopLevel) {
+  _onTargetDestroyed({ targetFront }) {
+    if (targetFront.isTopLevel) {
       this.proxy.disconnect();
       this.proxy = null;
     } else {
diff --git a/devtools/shared/resources/legacy-listeners/console-messages.js b/devtools/shared/resources/legacy-listeners/console-messages.js
index a1ad75d299a7..b913b5723557 100644
--- a/devtools/shared/resources/legacy-listeners/console-messages.js
+++ b/devtools/shared/resources/legacy-listeners/console-messages.js
@@ -6,9 +6,7 @@
 
 module.exports = async function({
   targetList,
-  targetType,
   targetFront,
-  isTopLevel,
   isFissionEnabledOnContentToolbox,
   onAvailable,
 }) {
@@ -20,9 +18,9 @@ module.exports = async function({
   const isContentToolbox = targetList.targetFront.isLocalTab;
   const listenForFrames = isContentToolbox && isFissionEnabledOnContentToolbox;
   const isAllowed =
-    isTopLevel ||
-    targetType === targetList.TYPES.PROCESS ||
-    (targetType === targetList.TYPES.FRAME && listenForFrames);
+    targetFront.isTopLevel ||
+    targetFront.targetType === targetList.TYPES.PROCESS ||
+    (targetFront.targetType === targetList.TYPES.FRAME && listenForFrames);
 
   if (!isAllowed) {
     return;
diff --git a/devtools/shared/resources/legacy-listeners/error-messages.js b/devtools/shared/resources/legacy-listeners/error-messages.js
index e85284c8c4a6..9dd14e10f183 100644
--- a/devtools/shared/resources/legacy-listeners/error-messages.js
+++ b/devtools/shared/resources/legacy-listeners/error-messages.js
@@ -6,9 +6,7 @@
 
 module.exports = async function({
   targetList,
-  targetType,
   targetFront,
-  isTopLevel,
   isFissionEnabledOnContentToolbox,
   onAvailable,
 }) {
@@ -20,9 +18,9 @@ module.exports = async function({
   const isContentToolbox = targetList.targetFront.isLocalTab;
   const listenForFrames = isContentToolbox && isFissionEnabledOnContentToolbox;
   const isAllowed =
-    isTopLevel ||
-    targetType === targetList.TYPES.PROCESS ||
-    (targetType === targetList.TYPES.FRAME && listenForFrames);
+    targetFront.isTopLevel ||
+    targetFront.targetType === targetList.TYPES.PROCESS ||
+    (targetFront.targetType === targetList.TYPES.FRAME && listenForFrames);
 
   if (!isAllowed) {
     return;
diff --git a/devtools/shared/resources/legacy-listeners/platform-messages.js b/devtools/shared/resources/legacy-listeners/platform-messages.js
index 681fd44c7b02..1dcfdfeed7f5 100644
--- a/devtools/shared/resources/legacy-listeners/platform-messages.js
+++ b/devtools/shared/resources/legacy-listeners/platform-messages.js
@@ -4,17 +4,13 @@
 
 "use strict";
 
-module.exports = async function({
-  targetList,
-  targetType,
-  targetFront,
-  isTopLevel,
-  onAvailable,
-}) {
+module.exports = async function({ targetList, targetFront, onAvailable }) {
   // Only allow the top level target and processes.
   // Frames can be ignored as logMessage are never sent to them anyway.
   // Also ignore workers as they are not supported yet. (see bug 1592584)
-  const isAllowed = isTopLevel || targetType === targetList.TYPES.PROCESS;
+  const isAllowed =
+    targetFront.isTopLevel ||
+    targetFront.targetType === targetList.TYPES.PROCESS;
   if (!isAllowed) {
     return;
   }
diff --git a/devtools/shared/resources/legacy-listeners/root-node.js b/devtools/shared/resources/legacy-listeners/root-node.js
index 6b048a8915b4..4e1ce54a6082 100644
--- a/devtools/shared/resources/legacy-listeners/root-node.js
+++ b/devtools/shared/resources/legacy-listeners/root-node.js
@@ -4,14 +4,8 @@
 
 "use strict";
 
-module.exports = async function({
-  targetList,
-  targetType,
-  targetFront,
-  isTopLevel,
-  onAvailable,
-}) {
-  if (!isTopLevel) {
+module.exports = async function({ targetList, targetFront, onAvailable }) {
+  if (!targetFront.isTopLevel) {
     return;
   }
 
diff --git a/devtools/shared/resources/resource-watcher.js b/devtools/shared/resources/resource-watcher.js
index 7ac5811759dc..497ed9638f4a 100644
--- a/devtools/shared/resources/resource-watcher.js
+++ b/devtools/shared/resources/resource-watcher.js
@@ -136,21 +136,12 @@ class ResourceWatcher {
   /**
    * Method called by the TargetList for each already existing or target which has just been created.
    *
-   * @param {string} type
-   *        One of the string of TargetList.TYPES to describe which
-   *        type of target is available.
    * @param {Front} targetFront
    *        The Front of the target that is available.
    *        This Front inherits from TargetMixin and is typically
    *        composed of a BrowsingContextTargetFront or ContentProcessTargetFront.
-   * @param {boolean} isTopLevel
-   *        If true, means that this is the top level target.
-   *        This typically happens on startup, providing the current
-   *        top level target. But also on navigation, when we navigate
-   *        to an URL which has to be loaded in a distinct process.
-   *        A new top level target is created.
    */
-  async _onTargetAvailable({ type, targetFront, isTopLevel }) {
+  async _onTargetAvailable({ targetFront }) {
     // For each resource type...
     for (const resourceType of Object.values(ResourceWatcher.TYPES)) {
       // ...which has at least one listener...
@@ -158,12 +149,7 @@ class ResourceWatcher {
         continue;
       }
       // ...request existing resource and new one to come from this one target
-      await this._watchResourcesForTarget(
-        type,
-        targetFront,
-        isTopLevel,
-        resourceType
-      );
+      await this._watchResourcesForTarget(targetFront, resourceType);
     }
   }
 
@@ -171,7 +157,7 @@ class ResourceWatcher {
    * Method called by the TargetList when a target has just been destroyed
    * See _onTargetAvailable for arguments, they are the same.
    */
-  _onTargetDestroyed({ type, targetFront }) {
+  _onTargetDestroyed({ targetFront }) {
     //TODO: Is there a point in doing anything?
     //
     // We could remove the available/destroyed event, but as the target is destroyed
@@ -269,14 +255,7 @@ class ResourceWatcher {
     for (const targetType of this.targetList.ALL_TYPES) {
       // XXX: May be expose a getReallyAllTarget() on TargetList?
       for (const target of this.targetList.getAllTargets(targetType)) {
-        promises.push(
-          this._watchResourcesForTarget(
-            targetType,
-            target,
-            target == this.targetList.targetFront,
-            resourceType
-          )
-        );
+        promises.push(this._watchResourcesForTarget(target, resourceType));
       }
     }
     await Promise.all(promises);
@@ -286,7 +265,7 @@ class ResourceWatcher {
    * Call backward compatibility code from `LegacyListeners` in order to listen for a given
    * type of resource from a given target.
    */
-  _watchResourcesForTarget(targetType, targetFront, isTopLevel, resourceType) {
+  _watchResourcesForTarget(targetFront, resourceType) {
     const onAvailable = this._onResourceAvailable.bind(
       this,
       targetFront,
@@ -294,9 +273,7 @@ class ResourceWatcher {
     );
     return LegacyListeners[resourceType]({
       targetList: this.targetList,
-      targetType,
       targetFront,
-      isTopLevel,
       isFissionEnabledOnContentToolbox: this.contentToolboxFissionPrefValue,
       onAvailable,
     });
@@ -367,13 +344,11 @@ const LegacyListeners = {
     .PLATFORM_MESSAGES]: require("devtools/shared/resources/legacy-listeners/platform-messages"),
   async [ResourceWatcher.TYPES.DOCUMENT_EVENTS]({
     targetList,
-    targetType,
     targetFront,
-    isTopLevel,
     onAvailable,
   }) {
     // DocumentEventsListener of webconsole handles only top level document.
-    if (!isTopLevel) {
+    if (!targetFront.isTopLevel) {
       return;
     }
 
diff --git a/devtools/shared/resources/target-list.js b/devtools/shared/resources/target-list.js
index aa275d9ffa44..6f9ac3a5de66 100644
--- a/devtools/shared/resources/target-list.js
+++ b/devtools/shared/resources/target-list.js
@@ -127,28 +127,22 @@ class TargetList {
 
     // Map the descriptor typeName to a target type.
     const targetType = this.getTargetType(targetFront);
-    const isTopLevel = targetFront == this.targetFront;
 
     targetFront.setTargetType(targetType);
-    targetFront.setIsTopLevel(isTopLevel);
+    targetFront.setIsTopLevel(targetFront == this.targetFront);
 
     this._targets.add(targetFront);
 
     // Notify the target front creation listeners
     await this._createListeners.emitAsync(targetType, {
-      type: targetType,
       targetFront,
-      isTopLevel,
       isTargetSwitching,
     });
   }
 
   _onTargetDestroyed(targetFront, isTargetSwitching = false) {
-    const targetType = targetFront.targetType;
-    this._destroyListeners.emit(targetType, {
-      type: targetType,
+    this._destroyListeners.emit(targetFront.targetType, {
       targetFront,
-      isTopLevel: targetFront.isTopLevel,
       isTargetSwitching,
     });
     this._targets.delete(targetFront);
@@ -301,10 +295,8 @@ class TargetList {
    *        The type of target to listen for. Constant of TargetList.TYPES.
    * @param {Function} onAvailable
    *        Callback fired when a target has been just created or was already available.
-   *        The function is called with three arguments:
-   *        - {String} type: The target type
+   *        The function is called with the following arguments:
    *        - {TargetFront} targetFront: The target Front
-   *        - {Boolean} isTopLevel: Is this target the top level one?
    *        - {Boolean} isTargetSwitching: Is this target relates to a navigation and
    *                    this replaced a previously available target, this flag will be true
    * @param {Function} onDestroy
@@ -327,9 +319,7 @@ class TargetList {
           // which may setup things regarding the existing targets
           // and listen callsite may care about the full initialization
           await onAvailable({
-            type: targetFront.targetType,
             targetFront,
-            isTopLevel: targetFront == this.targetFront,
             isTargetSwitching: false,
           });
         } catch (e) {
diff --git a/devtools/shared/resources/tests/browser_target_list_frames.js b/devtools/shared/resources/tests/browser_target_list_frames.js
index 0515e66a4353..b268bd28b42a 100644
--- a/devtools/shared/resources/tests/browser_target_list_frames.js
+++ b/devtools/shared/resources/tests/browser_target_list_frames.js
@@ -61,15 +61,15 @@ async function testBrowserFrames(mainRoot) {
 
   // Assert that watchTargets will call the create callback for all existing frames
   const targets = [];
-  const onAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onAvailable = ({ targetFront }) => {
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.FRAME,
       "We are only notified about frame targets"
     );
     ok(
-      targetFront == target ? isTopLevel : !isTopLevel,
-      "isTopLevel argument is correct"
+      targetFront == target ? targetFront.isTopLevel : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
     );
     targets.push(targetFront);
   };
@@ -125,15 +125,15 @@ async function testTabFrames(mainRoot) {
 
   // Assert that watchTargets will call the create callback for all existing frames
   const targets = [];
-  const onAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onAvailable = ({ targetFront }) => {
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.FRAME,
       "We are only notified about frame targets"
     );
     ok(
-      targetFront == target ? isTopLevel : !isTopLevel,
-      "isTopLevel argument is correct"
+      targetFront == target ? targetFront.isTopLevel : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
     );
     targets.push(targetFront);
   };
diff --git a/devtools/shared/resources/tests/browser_target_list_preffedoff.js b/devtools/shared/resources/tests/browser_target_list_preffedoff.js
index 72aa2268e61c..8a6ef0986526 100644
--- a/devtools/shared/resources/tests/browser_target_list_preffedoff.js
+++ b/devtools/shared/resources/tests/browser_target_list_preffedoff.js
@@ -60,7 +60,7 @@ async function testPreffedOffMainProcess(mainRoot, mainProcess) {
   );
 
   const processTargets = [];
-  const onProcessAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onProcessAvailable = ({ targetFront }) => {
     processTargets.push(targetFront);
   };
   await targetList.watchTargets([TargetList.TYPES.PROCESS], onProcessAvailable);
@@ -68,13 +68,16 @@ async function testPreffedOffMainProcess(mainRoot, mainProcess) {
   targetList.unwatchTargets([TargetList.TYPES.PROCESS], onProcessAvailable);
 
   const frameTargets = [];
-  const onFrameAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onFrameAvailable = ({ targetFront }) => {
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.FRAME,
       "We are only notified about frame targets"
     );
-    ok(isTopLevel, "We are only notified about the top level target");
+    ok(
+      targetFront.isTopLevel,
+      "We are only notified about the top level target"
+    );
     frameTargets.push(targetFront);
   };
   await targetList.watchTargets([TargetList.TYPES.FRAME], onFrameAvailable);
@@ -123,13 +126,16 @@ async function testPreffedOffTab(mainRoot) {
   targetList.unwatchTargets([TargetList.TYPES.PROCESS], onProcessAvailable);
 
   const frameTargets = [];
-  const onFrameAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onFrameAvailable = ({ targetFront }) => {
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.FRAME,
       "We are only notified about frame targets"
     );
-    ok(isTopLevel, "We are only notified about the top level target");
+    ok(
+      targetFront.isTopLevel,
+      "We are only notified about the top level target"
+    );
     frameTargets.push(targetFront);
   };
   await targetList.watchTargets([TargetList.TYPES.FRAME], onFrameAvailable);
diff --git a/devtools/shared/resources/tests/browser_target_list_processes.js b/devtools/shared/resources/tests/browser_target_list_processes.js
index 4d517f932b2d..3267cb9b7c44 100644
--- a/devtools/shared/resources/tests/browser_target_list_processes.js
+++ b/devtools/shared/resources/tests/browser_target_list_processes.js
@@ -62,22 +62,22 @@ async function testProcesses(targetList, target) {
 
   // Assert that watchTargets will call the create callback for all existing frames
   const targets = new Set();
-  const onAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onAvailable = ({ targetFront }) => {
     if (targets.has(targetFront)) {
       ok(false, "The same target is notified multiple times via onAvailable");
     }
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.PROCESS,
       "We are only notified about process targets"
     );
     ok(
-      targetFront == target ? isTopLevel : !isTopLevel,
-      "isTopLevel argument is correct"
+      targetFront == target ? targetFront.isTopLevel : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
     );
     targets.add(targetFront);
   };
-  const onDestroyed = ({ type, targetFront, isTopLevel }) => {
+  const onDestroyed = ({ targetFront }) => {
     if (!targets.has(targetFront)) {
       ok(
         false,
@@ -85,12 +85,12 @@ async function testProcesses(targetList, target) {
       );
     }
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.PROCESS,
       "We are only notified about process targets"
     );
     ok(
-      !isTopLevel,
+      !targetFront.isTopLevel,
       "We are never notified about the top level target destruction"
     );
     targets.delete(targetFront);
@@ -115,7 +115,7 @@ async function testProcesses(targetList, target) {
   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 = ({ type, targetFront, isTopLevel }) => {
+    const onAvailable2 = ({ targetFront }) => {
       if (previousTargets.has(targetFront)) {
         return;
       }
@@ -139,7 +139,7 @@ async function testProcesses(targetList, target) {
   // Assert that onDestroyed is called for destroyed processes
   const onProcessDestroyed = new Promise(resolve => {
     const onAvailable3 = () => {};
-    const onDestroyed3 = ({ type, targetFront, isTopLevel }) => {
+    const onDestroyed3 = ({ targetFront }) => {
       resolve(targetFront);
       targetList.unwatchTargets(
         [TargetList.TYPES.PROCESS],
diff --git a/devtools/shared/resources/tests/browser_target_list_switchToTarget.js b/devtools/shared/resources/tests/browser_target_list_switchToTarget.js
index f88e1af7fe74..1406debfd587 100644
--- a/devtools/shared/resources/tests/browser_target_list_switchToTarget.js
+++ b/devtools/shared/resources/tests/browser_target_list_switchToTarget.js
@@ -47,22 +47,19 @@ async function testSwitchToTarget(client) {
 
   const frameTargets = [];
   let currentTarget = firstTarget;
-  const onFrameAvailable = ({
-    type,
-    targetFront,
-    isTopLevel,
-    isTargetSwitching,
-  }) => {
+  const onFrameAvailable = ({ targetFront, isTargetSwitching }) => {
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.FRAME,
       "We are only notified about frame targets"
     );
     ok(
-      targetFront == currentTarget ? isTopLevel : !isTopLevel,
-      "isTopLevel argument is correct"
+      targetFront == currentTarget
+        ? targetFront.isTopLevel
+        : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
     );
-    if (isTopLevel) {
+    if (targetFront.isTopLevel) {
       // When calling watchTargets, this will be false, but it will be true when calling switchToTarget
       is(
         isTargetSwitching,
@@ -75,22 +72,19 @@ async function testSwitchToTarget(client) {
     frameTargets.push(targetFront);
   };
   const destroyedTargets = [];
-  const onFrameDestroyed = ({
-    type,
-    targetFront,
-    isTopLevel,
-    isTargetSwitching,
-  }) => {
+  const onFrameDestroyed = ({ targetFront, isTargetSwitching }) => {
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.FRAME,
       "target-destroyed: We are only notified about frame targets"
     );
     ok(
-      targetFront == firstTarget ? isTopLevel : !isTopLevel,
-      "target-destroyed: isTopLevel argument is correct"
+      targetFront == firstTarget
+        ? targetFront.isTopLevel
+        : !targetFront.isTopLevel,
+      "target-destroyed: isTopLevel property is correct"
     );
-    if (isTopLevel) {
+    if (targetFront.isTopLevel) {
       is(
         isTargetSwitching,
         true,
diff --git a/devtools/shared/resources/tests/browser_target_list_watchTargets.js b/devtools/shared/resources/tests/browser_target_list_watchTargets.js
index 4d3808dd408b..a8e2eda98d08 100644
--- a/devtools/shared/resources/tests/browser_target_list_watchTargets.js
+++ b/devtools/shared/resources/tests/browser_target_list_watchTargets.js
@@ -45,22 +45,22 @@ async function testWatchTargets(mainRoot) {
     "Check that onAvailable is called for processes already created *before* the call to watchTargets"
   );
   const targets = new Set();
-  const onAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onAvailable = ({ targetFront }) => {
     if (targets.has(targetFront)) {
       ok(false, "The same target is notified multiple times via onAvailable");
     }
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.PROCESS,
       "We are only notified about process targets"
     );
     ok(
-      targetFront == target ? isTopLevel : !isTopLevel,
-      "isTopLevel argument is correct"
+      targetFront == target ? targetFront.isTopLevel : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
     );
     targets.add(targetFront);
   };
-  const onDestroyed = ({ type, targetFront, isTopLevel }) => {
+  const onDestroyed = ({ targetFront }) => {
     if (!targets.has(targetFront)) {
       ok(
         false,
@@ -68,12 +68,12 @@ async function testWatchTargets(mainRoot) {
       );
     }
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.PROCESS,
       "We are only notified about process targets"
     );
     ok(
-      !isTopLevel,
+      !targetFront.isTopLevel,
       "We are not notified about the top level target destruction"
     );
     targets.delete(targetFront);
@@ -105,7 +105,7 @@ async function testWatchTargets(mainRoot) {
   );
   const previousTargets = new Set(targets);
   const onProcessCreated = new Promise(resolve => {
-    const onAvailable2 = ({ type, targetFront, isTopLevel }) => {
+    const onAvailable2 = ({ targetFront }) => {
       if (previousTargets.has(targetFront)) {
         return;
       }
@@ -130,7 +130,7 @@ async function testWatchTargets(mainRoot) {
   // Assert that onDestroyed is called for destroyed processes
   const onProcessDestroyed = new Promise(resolve => {
     const onAvailable3 = () => {};
-    const onDestroyed3 = ({ type, targetFront, isTopLevel }) => {
+    const onDestroyed3 = ({ targetFront }) => {
       resolve(targetFront);
       targetList.unwatchTargets(
         [TargetList.TYPES.PROCESS],
@@ -185,22 +185,25 @@ async function testContentProcessTarget(mainRoot) {
   // as listening for additional target is only enable for the parent process target.
   // See bug 1593928.
   const targets = new Set();
-  const onAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onAvailable = ({ targetFront }) => {
     if (targets.has(targetFront)) {
       // This may fail if the top level target is reported by LegacyImplementation
       // to TargetList and emits an available event for it.
       ok(false, "The same target is notified multiple times via onAvailable");
     }
     is(
-      type,
+      targetFront.targetType,
       TargetList.TYPES.PROCESS,
       "We are only notified about process targets"
     );
     is(targetFront, target, "This is the existing top level target");
-    ok(isTopLevel, "We are only notified about the top level target");
+    ok(
+      targetFront.isTopLevel,
+      "We are only notified about the top level target"
+    );
     targets.add(targetFront);
   };
-  const onDestroyed = ({ type, targetFront, isTopLevel }) => {
+  const onDestroyed = _ => {
     ok(false, "onDestroyed should never be called in this test");
   };
   await targetList.watchTargets(
@@ -235,7 +238,7 @@ async function testThrowingInOnAvailable(mainRoot) {
   );
   const targets = new Set();
   let thrown = false;
-  const onAvailable = ({ type, targetFront, isTopLevel }) => {
+  const onAvailable = ({ targetFront }) => {
     if (!thrown) {
       thrown = true;
       throw new Error("Force an exception when processing the first target");
diff --git a/devtools/shared/resources/tests/browser_target_list_workers.js b/devtools/shared/resources/tests/browser_target_list_workers.js
index b6764d57da8e..0fcb0159f045 100644
--- a/devtools/shared/resources/tests/browser_target_list_workers.js
+++ b/devtools/shared/resources/tests/browser_target_list_workers.js
@@ -114,16 +114,16 @@ async function testBrowserWorkers(mainRoot) {
     "Check that watchTargets will call the create callback for all existing workers"
   );
   const targets = [];
-  const onAvailable = async ({ type, targetFront, isTopLevel }) => {
+  const onAvailable = async ({ targetFront }) => {
     ok(
-      type === TYPES.WORKER ||
-        type === TYPES.SHARED_WORKER ||
-        type === TYPES.SERVICE_WORKER,
+      targetFront.targetType === TYPES.WORKER ||
+        targetFront.targetType === TYPES.SHARED_WORKER ||
+        targetFront.targetType === TYPES.SERVICE_WORKER,
       "We are only notified about worker targets"
     );
     ok(
-      targetFront == target ? isTopLevel : !isTopLevel,
-      "isTopLevel argument is correct"
+      targetFront == target ? targetFront.isTopLevel : !targetFront.isTopLevel,
+      "isTopLevel property is correct"
     );
     targets.push(targetFront);
   };
@@ -157,7 +157,7 @@ async function testBrowserWorkers(mainRoot) {
 
   // Create a new worker and see if the worker target is reported
   const onWorkerCreated = new Promise(resolve => {
-    const onAvailable2 = async ({ type, targetFront, isTopLevel }) => {
+    const onAvailable2 = async ({ targetFront }) => {
       if (targets.includes(targetFront)) {
         return;
       }
@@ -213,9 +213,13 @@ async function testTabWorkers(mainRoot, tab) {
 
   // Assert that watchTargets will call the create callback for all existing workers
   const targets = [];
-  const onAvailable = async ({ type, targetFront, isTopLevel }) => {
-    is(type, TYPES.WORKER, "We are only notified about worker targets");
-    ok(!isTopLevel, "The workers are never top level");
+  const onAvailable = async ({ targetFront }) => {
+    is(
+      targetFront.targetType,
+      TYPES.WORKER,
+      "We are only notified about worker targets"
+    );
+    ok(!targetFront.isTopLevel, "The workers are never top level");
     targets.push(targetFront);
   };
   await targetList.watchTargets([TYPES.WORKER], onAvailable);
diff --git a/toolkit/components/extensions/ExtensionParent.jsm b/toolkit/components/extensions/ExtensionParent.jsm
index 1a41901e7294..229116f24796 100644
--- a/toolkit/components/extensions/ExtensionParent.jsm
+++ b/toolkit/components/extensions/ExtensionParent.jsm
@@ -787,8 +787,8 @@ class DevToolsExtensionPageContextParent extends ExtensionPageContextParent {
     super.shutdown();
   }
 
-  async _onTargetAvailable({ targetFront, isTopLevel }) {
-    if (!isTopLevel) {
+  async _onTargetAvailable({ targetFront }) {
+    if (!targetFront.isTopLevel) {
       return;
     }