This document describes the user agent string used in Firefox 4 and later and applications based on Gecko 2.0 and later. For a breakdown of changes to the string in Gecko 2.0, seeFinal User Agent string for Firefox 4 (blog post). See also this document onuser agent sniffing and thisHacks blog post.

General form

The UA string of Firefox itself is broken down into four components:

Mozilla/5.0 (platform; rv:gecko-version) Gecko/gecko-trail Firefox/firefox-version

• Mozilla/5.0 is the general token that says the browser is Mozilla compatible, and is common to almost every browser today.

• platform describes the native platform the browser is running on (e.g., Windows, Mac, Linux or Android), and whether or not it's a mobile phone. Firefox OS phones sayMobile; the web is the platform. Note thatplatform can consist of multiple;-separated tokens. See below for further details and examples.

• rv:gecko-version indicates the release version of Gecko (such as17.0).

• Gecko/gecko-trail indicates that the browser is based on Gecko.

• On Desktop,gecko-trail is the fixed string20100101.

• Firefox/firefox-version indicates the browser is Firefox, and provides the version (such as17.0).

• From Firefox 10 on mobile,gecko-trail is the same asfirefox-version.

For other products based on Gecko, the string can take one of two forms, where the tokens have the same meaning except those noted below:

Mozilla/5.0 (platform; rv:gecko-version) Gecko/gecko-trail app-name/app-versionMozilla/5.0 (platform; rv:gecko-version) Gecko/gecko-trail Firefox/firefox-version app-name/app-version

• app-name/app-version indicates the application name and version. For instance, this could beCamino/2.1.1, orSeaMonkey/2.7.1.
• Firefox/firefox-version is an optional compatibility token that some Gecko-based browsers may choose to incorporate, to achieve maximum compatibility with websites that expect Firefox.firefox-version will generally represent the equivalent Firefox release corresponding to the given Gecko version. Some Gecko-based browsers may not opt into using this token; for this reason, sniffers should be looking for Gecko — not Firefox!

Mobile and Tablet indicators

Theplatform part of the UA string indicates if Firefox is running on a phone-sized or tablet device. When Firefox runs on a device that has the phone form factor, there is aMobile; token in theplatform part of the UA string. When Firefox runs on a tablet device, there is aTablet; token in theplatform part of the UA string instead. For example:

Mozilla/5.0 (Android 4.4; Mobile; rv:41.0) Gecko/41.0 Firefox/41.0Mozilla/5.0 (Android 4.4; Tablet; rv:41.0) Gecko/41.0 Firefox/41.0

The preferred way to target content to a device form factor is to use CSS Media Queries. However, if you use UA sniffing to target content to a device form factor, please look forMobi (to include Opera Mobile, which uses "Mobi") for the phone form factor and donot assume any correlation between "Android" and the device form factor. This way, your code will work if/when Firefox ships on other phone/tablet operating systems or Android is used for laptops. Also, please use touch detection to find touch devices rather than looking for "Mobi" or "Tablet", since there may be touch devices which are not tablets.

Windows

Windows user agents have the following variations, wherex.y is the Windows NT version (for instance, Windows NT 6.1).

macOS

Here,x.y is the version of macOS (for instance, macOS 10.15). Starting in Firefox 87, Firefox caps the reported macOS version number to 10.15, so macOS 11.0 Big Sur and later will be reported as "10.15" in the User-Agent string. ARM-based Macs will be reported as "Intel" in the User-Agent string.

Linux

Linux is a more diverse platform. Your distribution of Linux might include an extension that changes your user-agent. A few common examples are given below.

Firefox for Android

Firefox for Android contains the Android version as part of theplatform token. For increased interoperability, if the browser is running on a version below 4 it will report 4.4. Android versions 4 and above report the version accurately. Note that the same Gecko—with the same capabilities—is shipped to all versions of Android.

Focus for Android

From version 1, Focus is powered by Android WebView and uses the following user agent string format:

Mozilla/5.0 (Linux; <Android Version> <Build Tag etc.>) AppleWebKit/<WebKit Rev> (KHTML, like Gecko) Version/4.0 Focus/<focus version> Chrome/<Chrome Rev> Mobile Safari/<WebKit Rev>

Tablet versions on WebView mirror mobile, but do not contain aMobile token.

Starting in Version 6, users can opt into using a GeckoView-based Focus for Android with a hidden preference: it uses a GeckoView UA string to advertise Gecko compatibility.

The Klar user agent is the same asFocus.

Firefox for iOS

Firefox for iOS uses the default Mobile Safari UA string, with an additionalFxiOS/<version> token on iPod and iPhone, similar to howChrome for iOS identifies itself.

On iPad, the user agent string appears identically as Safari. For various issues related to the non-inclusion ofFxiOS on iOS, seemozilla-mobile/firefox-ios#6620.

Focus for iOS

Version 7 of Focus for iOS uses a user agent string with the following format:

Mozilla/5.0 (iPhone; CPU iPhone OS 12_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) FxiOS/7.0.4 Mobile/16B91 Safari/605.1.15

Note: this user agent was retrieved from an iPhone XR simulator and may be different on device.

Firefox for Fire TV

Version 3 (and probably earlier) of Firefox for Fire TV use a user agent string with the following format:

Mozilla/5.0 (Linux; <Android version>) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Focus/<firefox-version> Chrome/<Chrome Rev> Safari/<WebKit Rev>

Firefox for Echo Show

From version 1.1, Firefox for Echo Show uses a user agent string with the following format:

Mozilla/5.0 (Linux; <Android version>) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Focus/<firefox-version> Chrome/<Chrome Rev> Safari/<WebKit Rev>

Firefox OS

Device-specific user agent strings

Although it isstrongly discouraged by Mozilla, some handset manufacturers unfortunately include a token in their device's UA string that represents their device id. If this is the case, the Firefox OS UA string will look like the device-specific string in the table above, wherennnn; is the manufacturer's code for the device (seeGuidelines). Some of them we have noticed are of the form "NexusOne;", "ZTEOpen;", or "Open C;" (note that putting space is also discouraged). We provide this information to assist with your UA detection logic, but Mozilla discourages the detection of a device id in UA strings.

Here is a JavaScript regular expression that will detect all mobile devices, including devices with a device id in their UA string:

/mobi/i;

Thei makes it case-insensitive, andmobi matches all mobile browsers.

Firefox OS version number

While the version number for Firefox OS is not included in the UA string, it is possible to infer version information from the Gecko version number present in the UA string.

Firefox OS has a four-digit version number:X.X.X.Y. The first two digits are owned by the Mozilla product team and denote versions with new features (eg: v1.1, 1.2, etc.). The third digit is incremented with regular version tags (about every 6 weeks) for security updates, and the fourth is owned by the OEM.

See also

• Recommendations onsniffing the UA string for cross-browser support
• navigator.userAgent