diff --git a/devtools/client/debugger/src/client/firefox.js b/devtools/client/debugger/src/client/firefox.js
index a1e92c5c58f3..97b382e2ea4f 100644
--- a/devtools/client/debugger/src/client/firefox.js
+++ b/devtools/client/debugger/src/client/firefox.js
@@ -4,27 +4,31 @@
 
 // @flow
 
-import { setupCommands, clientCommands } from "./firefox/commands";
-import { setupEvents, clientEvents } from "./firefox/events";
+import {
+  setupCommands,
+  setupCommandsTopTarget,
+  clientCommands,
+} from "./firefox/commands";
+import {
+  setupEvents,
+  setupEventsTopTarget,
+  clientEvents,
+} from "./firefox/events";
 import { features, prefs } from "../utils/prefs";
 
 export async function onConnect(connection: any, actions: Object) {
   const { debuggerClient, targetList } = connection;
+  setupCommands({ debuggerClient });
+  setupEvents({ actions, debuggerClient });
+
   const currentTarget = targetList.targetFront;
   const threadFront = currentTarget.threadFront;
 
   if (!currentTarget || !threadFront || !debuggerClient) {
     return;
   }
-
-  setupCommands({
-    threadFront,
-    currentTarget,
-    debuggerClient,
-  });
-
-  setupEvents({ threadFront, currentTarget, actions, debuggerClient });
-
+  setupCommandsTopTarget(currentTarget);
+  setupEventsTopTarget(currentTarget);
   currentTarget.on("will-navigate", actions.willNavigate);
   currentTarget.on("navigate", actions.navigated);
 
diff --git a/devtools/client/debugger/src/client/firefox/commands.js b/devtools/client/debugger/src/client/firefox/commands.js
index c739fc1f0c47..41297aba421f 100644
--- a/devtools/client/debugger/src/client/firefox/commands.js
+++ b/devtools/client/debugger/src/client/firefox/commands.js
@@ -52,20 +52,21 @@ let eventBreakpoints: ?EventListenerActiveList;
 const CALL_STACK_PAGE_SIZE = 1000;
 
 type Dependencies = {
-  threadFront: ThreadFront,
-  currentTarget: Target,
   debuggerClient: DebuggerClient,
 };
 
 function setupCommands(dependencies: Dependencies) {
-  currentThreadFront = dependencies.threadFront;
-  currentTarget = dependencies.currentTarget;
   debuggerClient = dependencies.debuggerClient;
   targets = {};
   sourceActors = {};
   breakpoints = {};
 }
 
+function setupCommandsTopTarget(targetFront: Target) {
+  currentTarget = targetFront;
+  currentThreadFront = targetFront.threadFront;
+}
+
 function createObjectFront(grip: Grip): ObjectFront {
   if (!grip.actor) {
     throw new Error("Actor is missing");
@@ -598,4 +599,4 @@ const clientCommands = {
   fetchAncestorFramePositions,
 };
 
-export { setupCommands, clientCommands };
+export { setupCommands, setupCommandsTopTarget, clientCommands };
diff --git a/devtools/client/debugger/src/client/firefox/events.js b/devtools/client/debugger/src/client/firefox/events.js
index a86232b2d516..f3c55f360109 100644
--- a/devtools/client/debugger/src/client/firefox/events.js
+++ b/devtools/client/debugger/src/client/firefox/events.js
@@ -25,14 +25,13 @@ const {
 } = require("devtools/client/shared/workers-listener.js");
 
 type Dependencies = {
-  threadFront: ThreadFront,
-  currentTarget: Target,
   actions: typeof Actions,
   debuggerClient: DebuggerClient,
 };
 
 let actions: typeof Actions;
 let isInterrupted: boolean;
+let workersListener: Object;
 
 function addThreadEventListeners(thread: ThreadFront) {
   Object.keys(clientEvents).forEach(eventName => {
@@ -45,16 +44,21 @@ function attachAllTargets(currentTarget: Target) {
 }
 
 function setupEvents(dependencies: Dependencies) {
-  const { currentTarget, threadFront, debuggerClient } = dependencies;
+  const { debuggerClient } = dependencies;
   actions = dependencies.actions;
   sourceQueue.initialize(actions);
 
-  addThreadEventListeners(threadFront);
-  currentTarget.on("workerListChanged", () => threadListChanged());
   debuggerClient.mainRoot.on("processListChanged", () => threadListChanged());
 
-  if (features.windowlessServiceWorkers || attachAllTargets(currentTarget)) {
-    const workersListener = new WorkersListener(debuggerClient.mainRoot);
+  workersListener = new WorkersListener(debuggerClient.mainRoot);
+}
+
+function setupEventsTopTarget(targetFront: Target) {
+  targetFront.on("workerListChanged", () => threadListChanged());
+  addThreadEventListeners(targetFront.threadFront);
+
+  workersListener.removeListener();
+  if (features.windowlessServiceWorkers || attachAllTargets(targetFront)) {
     workersListener.addListener(() => threadListChanged());
   }
 }
@@ -130,4 +134,10 @@ const clientEvents = {
   replayFramePositions,
 };
 
-export { setupEvents, clientEvents, addThreadEventListeners, attachAllTargets };
+export {
+  setupEvents,
+  setupEventsTopTarget,
+  clientEvents,
+  addThreadEventListeners,
+  attachAllTargets,
+};