Firefox extension: Attempting to message content script throws an error

I have spent all day trying to figure this out and I seem to be getting nowhere, can someone share with me where I am going wrong?

I am trying to figure out how to correctly send a message, from a “background” script to a content script. I want to use onBeforeRequest() as the trigger event, so that when it happens a message is to sent to the content script to get some information from the pages DOM.

The DOM part is not present in this example, I am struggling to just establish a working messaging pattern.

manifest file:

	"name": "shell",
	"manifest_version": 2,
	"version": "1.0",

	"background": {"scripts": ["background.js"]},
	"content_scripts": [
		  "matches": ["<all_urls>"],
		  "js": ["content.js"]
	"permissions": ["tabs","activeTab", "webRequest", "<all_urls>"]

background.js file:

activeTab = browser.tabs.query({currentWindow: true,active: true,})

function sendMessageToTabs(activeTab) {
	for (const tab of activeTab) {
	  browser.tabs.sendMessage(, { greeting: "Hi from background script" })
		 .then((response) => {
			console.log("Message from the content script:");
browser.webRequest.onBeforeRequest.addListener(sendMessageToTabs, {urls:[""]});

Content.js file:

"use strict";

browser.runtime.onMessage.addListener((request) => {
  console.log("Message from the background script:");
  return Promise.resolve({ response: "Hi from content script" });

How to trigger the event

Once I load the extension, I can trigger the on onBeforeRequest() by visiting the “Car - Wikipedia” page of Wikipedia and clicking on the Vehicle part, right under the article profile picture, as shown HERE.

The problem I am having

Is that when the event triggers I get an error in the DevTools console:

TypeError: activeTab is not iterable

I tried a number of ways to solve this issue but it just persists. Any help or pointers would be amazing. Cheers.

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