Confusing message from firefox.com/pair on iOS

[joewalker]

Description

When signing up a new phone and linking it to an existing account, you're told to visit firefox.com/pair to link your account. If you do this on Firefox iOS on iPad you don't get the helpful message "use a computer" message.

Steps to reproduce

With Firefox on iPadOS, visit firefox.com/pair and observe the message.

Expected result

On Firefox on an iPhone you get the following message:

Connecting your mobile device with your Mozilla account
Open Firefox on your computer, visit firefox.com/pair, and follow the on-screen instructions to connect your mobile device.

Actual result

On Firefox on iPadOS you get this message:

Oops! It looks like you’re not using Firefox.
Switch to Firefox and open this page to connect another device.

Environment

Firefox 132.1 (47104)
iPadOS 18.1.1

┆Issue is synchronized with this Jira Task

[janbrasna]

On Firefox on iPadOS you get this message:

Oops! It looks like you’re not using Firefox.
Switch to Firefox and open this page to connect another device.

Basically Firefox on iPad pretends to be desktop Safari — so my guess is that's what's being detected.

A good countermeasure is to additionally look for coarse pointer or touch/drag events, that can tell the UA is only "pretending" to be desktop Safari, in which case a mobile device can be inferred and the same "Open Firefox on your computer" message served.

[janbrasna]

According to comments in the code used to detect the devices, it's a known issue:

fxa/packages/fxa-content-server/app/scripts/lib/user-agent.js

Lines 33 to 53 in 0234048

	* This does not work for latest iPad, see note above isDesktopFirefoxOnIpad.
	*
	* @returns {Boolean}
	*/
	isMobile() {
	return this.isIos() || this.isAndroid();
	},
	/**
	* iPads using FF iOS 13+ send a desktop UA.
	* The OS shows as a Mac, but 'Firefox iOS' in the UA family.
	*
	* NOTE, as of at least Sept 2024, this is no longer reliable.
	* The UA for iPad Safari exactly matches the UA for iPad Firefox
	* except for "Version" which is unreliable.
	*
	* @returns {Boolean}
	*/
	isDesktopFirefoxOnIpad() {
	return /Mac/.test(this.os.name) && /FxiOS/.test(this.ua);
	},

[janbrasna]

The culprit might be in outdated ua-parser-js used:

fxa/packages/fxa-content-server/package.json

Line 128 in 0234048

"ua-parser-js": "1.0.35",

According to faisalman/ua-parser-js@5ea9f0e this should work as of v2.0.0 — however there are a few breaking changes regarding mobile UAs: https://github.com/faisalman/ua-parser-js/releases/tag/2.0.0-alpha.2

EDIT: v2 changed licensing so its AGPL might be incompatible here.

In that case additional feature checks exist even in v1.0.x that help identify iPad by touch/drag capability: https://docs.uaparser.dev/api/main/idata/with-feature-check.html