Firefox user agent for Windows 10 and 11
Copy a Windows Firefox 158.0 reference string, compare the alternate desktop form, or find the Firefox 157 example below for an older request log. Use the checker in Firefox to see your own browser's UA.
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:158.0) Gecko/20100101 Firefox/158.0
At a glance
| Browser | Firefox 158.0 |
| Engine | Gecko 158.0 |
| Operating system | Windows 10 |
| Device | Desktop |
Other forms of this user agent
32-bit Firefox on 32-bit Windows, or ARM64 Windows 10
Mozilla/5.0 (Windows NT 10.0; rv:158.0) Gecko/20100101 Firefox/158.0Firefox 157 user agent example for older logs
Use this earlier example when reproducing a request recorded with Firefox/157.0. It is kept separately from the main reference so an updated browser example does not replace the string you are investigating. A copied UA is a test value, not proof of the browser that sent a request.
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:157.0) Gecko/20100101 Firefox/157.0What do rv:, Gecko and Firefox mean?
The rv: and Firefox/ tokens describe the Gecko and Firefox release versions. Gecko/20100101 is a fixed token in desktop Firefox; it is not the date the browser was installed or last updated.
The Windows example includes platform and architecture tokens. Treat them as client-reported compatibility information, not verified operating-system or hardware identity. Compare the alternate form above when investigating a particular request.
How to check your Firefox user agent
Open the checker in Firefox to see navigator.userAgent, or run the JavaScript below in that browser's console. A string copied from this page is an example and does not detect your installed browser.
For application compatibility, prefer feature detection. Extensions, privacy settings or an overridden UA can change what a browser reports, so parsing alone cannot establish its identity.
console.log(navigator.userAgent);String breakdown
| Fragment | Meaning |
|---|---|
Mozilla/5.0 | Historical compatibility token. Nearly every browser claims "Mozilla/5.0" so that old servers do not serve it broken pages. |
Windows NT 10.0 | Windows NT kernel 10.0 — Windows 10 or 11 (the value is frozen at 10.0). |
Win64 | 64-bit Windows. |
x64 | x86-64 (64-bit) CPU architecture. |
rv:158.0 | Revision/version marker: 158.0. |
Gecko/20100101 | Gecko engine token 20100101. Desktop Firefox freezes it at 20100101. |
Firefox/158.0 | Firefox, version 158.0. |
Use it in code
curl
curl -A "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:158.0) Gecko/20100101 Firefox/158.0" https://example.comPython (requests)
import requests
requests.get("https://example.com", headers={"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:158.0) Gecko/20100101 Firefox/158.0"})Playwright (Node.js)
const context = await browser.newContext({ userAgent: "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:158.0) Gecko/20100101 Firefox/158.0" });Source: Firefox user agent string reference · MDN: Firefox user agent string reference · checked September 2026