1852239 - Only Windows system fonts recognized in Private browsing

Status: RESOLVED WORKSFORME

(Core :: Privacy: Anti-Tracking, defect)

Description

[Fanolian]

+++ This bug was initially created as a clone of Bug #1852176 +++

Original report (slightly modified with info from bug 1852176 comment 6 and my own additions):

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/119.0

Steps to reproduce:

1. On Windows, install a user font which supports Khitan Small Script (Unicode block), e.g. Noto Fangsong KSSRotated or Unicode Last Resort Font.
2. With a new Nightly profile, browse https://wikisource.org/wiki/Kaesong_mirror_inscription in Private mode.

Actual results:

In Private browsing, everything is rendered only with Windows system fonts. Firefox's browser-wide font settings (Settings > General > Fonts > Advanced) and CSS font-family properties are all ignored.

Expected results:

The expected look should have no differences between in normal browsing and Private browsing.

:emk suggested in bug 1852176 comment 2 that the issue could be fixed, in Nightly, by setting layout.css.font-visibility.private to 3.
AFAIK this workaround no longer works since v118 because layout.css.font-visibility.private was removed in bug 1847599. Font visibility in Private Mode is now solely controlled by privacy.resistFingerprinting.pbmode, which will be enabled in Release channel in v118. (more info)

I understand that the current behaviour is expected. Is it, however, desirable for general users to disable all fingerprinting features just to display glyphs users prefer?

Thank you.

P.S. Sorry for not responding in the original report. I don't have the permission to comment in a closed bug.

Comment 1

[Fanolian]

Forgot to mention:

Before bug 1847599, I can display user-installed fonts in Private Browsing mode in Nightly by setting privacy.resistFingerprinting.pbmode to true and layout.css.font-visibility.private to 3.

Comment 2

[BugBot [:suhaib / :marco/ :calixte]]

:tjr, since you are the author of the regressor, bug 1847599, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 3

[[Away] Tom Schuster (MoCo)]

Font visibility in Private Mode is now solely controlled by privacy.resistFingerprinting.pbmode, which will be enabled in Release channel in v118.

The correct pref is privacy.fingerprintingProtection.pbmode btw.

Is it, however, desirable for general users to disable all fingerprinting features just to display glyphs users prefer?

That is not necessary. You can just disable fingerprinting protection for fonts by setting privacy.fingerprintingProtection.overrides to the string -FontVisibilityLangPack.

Comment 4

[Fanolian]

Thanks for the correction. And thanks for the pointer to overrides. I learnt something new today.