What can Firefox do on its own?
Firefox's Network Monitor lists the requests a page makes, and a request you pick can be sent again without any add-on [1][2]:
- Resend sends the request again as it was [1][2].
- Edit and Resend opens an editor where you change the method, address, headers or body, then press Send [1].
- Copy offers the request as a cURL command or as a fetch() call [2].
- Save All As HAR writes the listed requests to a HAR file [2].
- Block URL blocks the chosen address for later requests [2].
This is the quickest way to try one call you can already see. It works one request at a time, and which calls went wrong is for you to decide. The extensions below add more.
Which Firefox extensions test APIs?
These four are REST clients: you write a request and send it. The words in quotes are each listing's own summary, and the dates are the last update shown on Firefox Add-ons. They are listed in no order of merit.
| Extension | What its listing says | Last updated |
|---|---|---|
| RESTer | "A REST client for almost any web service." Sends requests with any method, address, body and headers; saves them in collections; keeps a history of requests and answers; Basic and OAuth 2 authorization [3] | August 2026 |
| RESTED | "A REST client for the rest of us." The common HTTP methods, headers, saved requests and collections, URL templates, Basic auth, and import from HAR or Postman collections [4] | December 2021 |
| Apier | "Fast API client for HTTP, GraphQL, SOAP, WebSocket, and Socket.IO." [5] | July 2026 |
| API Request Tester | "Test and debug API requests directly from your browser." [6] | June 2024 |
A client is the right tool when you already know which request to send. RequestFox starts from the other end: it watches what your web app really sends, so there is nothing to retype.
How do I record the API calls a page makes in Firefox?
- Add RequestFox from Firefox Add-ons. There is no account to make.
- Open the site you want to test. Open RequestFox's sidebar and press Start (or press Alt Shift S; Option Shift S on a Mac). The first time, Firefox asks you to allow access to the site.
- Use the page. Every fetch, XMLHttpRequest, WebSocket frame and server-sent event is listed as it starts, tied to the click or form submit that caused it.
- Read the flags. A call that failed, was slow, fired twice or hid an error inside a 200 OK is marked, and its card says why in plain words.
- Press Replay to send a call again, or Edit & Replay to change it first. While recording, the call goes through the page, with its cookies.
The full steps, with the search box and what to do when nothing shows up, are in How to record API calls. Sessions are kept in History, and you can export them as a HAR file, a Postman collection or an HTML report.
What does RequestFox not do in Firefox?
- Scripts that run before a request or after an answer, and rewriting a request or reply with a script, work in Chrome only: Firefox does not let extensions run code typed at runtime. Chaining values from one request to the next works in both.
- Firefox has no debugger API for extensions, so there is no slow-down for the whole tab. Use a mock rule's Slow or Throttle mode for one endpoint instead.
- Clicking a RequestFox notification opens the sidebar in the window you are looking at, which may not be the window being recorded.
- It sees what a browser tab sends. Mobile and desktop apps need a proxy-based tool, and there is no team workspace or cloud sync: share work as files.
Apart from these points, capture, flags, mocks, checks and exports are the same in Firefox as in Chrome. The feature list says which feature is Chrome only.
Which one should I use?
- To try one call you can already see: Edit and Resend in the Network Monitor. Nothing to install.
- To write requests by hand and keep them: a REST client such as RESTer or RESTED.
- To test your own web app as you click through it, with the broken calls found for you: RequestFox.
They fit together. Record in RequestFox, and use the built-in tools for a quick look at one request.
Sources
- Firefox Source Docs, "Network request details". Checked . firefox-source-docs.mozilla.org
- Firefox Source Docs, "Network request list". Checked . firefox-source-docs.mozilla.org
- Firefox Add-ons, RESTer. Checked . addons.mozilla.org
- Firefox Add-ons, RESTED. Checked . addons.mozilla.org
- Firefox Add-ons, Apier. Checked . addons.mozilla.org
- Firefox Add-ons, API Request Tester. Checked . addons.mozilla.org
Something here out of date? Add-ons change. Tell us at the address in the privacy policy and we will fix it.
Next
- Record API calls
Start, use the site, read the flags, keep the evidence.
- Replay and edit a request
Send a captured call again, as it was or changed.
- RequestFox vs DevTools Network
The judging and the history, or the raw live view.
- Mock an API response
Return your own answer, or make a call fail.