To try the thousands of add-ons available here, download Mozilla Firefox, a fast, free way to surf the Web!
CloseWelcome to Firefox Add-ons.
Choose from thousands of extra features and styles to make Firefox your own.
CloseReview for Live HTTP Headers by Firefox user 482764
Rated 4 out of 5 stars
It works fine in Firefox 44.0.2 on Windows 10. I just tested to see the HTTP headers of a test web page.
To create your own collections, you must have a Mozilla Add-ons account.