WebExtensions: browser.webRequest.onCompleted never fires - firefox-addon-webextensions

Question

I'm using the Firefox WebExtensions API with the following background script
var log = console.log.bind(console)
log('hello world from browser extension')
// https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/webRequest/onCompleted
var filter = { urls: '<all_urls>' }
var extraInfoSpec = ['tlsInfo', 'responseHeaders']
browser.webRequest.onCompleted.addListener(function(details){
log(`Woo got a request, here's the details!`, details)
}, filter, extraInfoSpec)
log('Added listener')
After loading the script from about:debugging, I see the following output in DevTools:
hello world from browser extension
I do not see any output- there is no data from browser.webRequest.onCompleted.addListener and there is no 'Added listener' message.
How do I make browser.webRequest.onCompleted work?
For completeness, my manifest.json is below:
{
"manifest_version": 2,
"name": "Test extension",
"version": "1.0",
"description": "Test extension.",
"icons": {
"48": "icons/border-48.png"
},
"content_scripts": [
{
"matches": ["<all_urls>"],
"js": ["content.js"]
}
],
"permissions": [
"webRequest",
"webRequestBlocking"
]
}

Answer 1

The webRequest API is only available to background scripts. You seem to using it inside a content script.
urls in var filter = { urls: '<all_urls>' } needs to be be an array ['<all_urls>'].
'tlsInfo' in extraInfoSpec doesn't exist, I don't know where it comes from.
You need to specify an additional <all_urls> permission in your manifest.
script.js
var filter = { urls: ['<all_urls>'] }
var extraInfoSpec = ['responseHeaders']
browser.webRequest.onCompleted.addListener(function(details){
console.log(`Woo got a request, here's the details!`, details)
}, filter, extraInfoSpec)
console.log('Added listener')
manifest.json
{
"manifest_version": 2,
"name": "Test extension",
"version": "1.0",
"description": "Test extension.",
"icons": {
"48": "icons/border-48.png"
},
"background": {
"scripts": ["script.js"]
},
"permissions": [
"webRequest",
"webRequestBlocking",
"<all_urls>"
]
}