1826419 - Detect font fingerprinting and tie it into the fingerprinting protections panel

Status: NEW

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

Description

[Tom Ritter [:tjr]]

We want to create a heuristic and behavior such as the following:

If we detect <50> attempts to detect a font blocked by font restrictions on a single document, using ReportBlockedFontFamilyName, we will indicate that this page has blocked a fingerprinter and we will <add an entry to the 'Blocked fingerprinters' panel saying "Font Fingerprinting" that hangs off the ETP panel accessed by the shield icon> and <increment the number of fingerprinters blocked that is shown on about:protections>.

I'm passing this bug to Martin to solidify the items <marked like this> to ensure I'm doing the right thing.

It's possible to see what fonts are blocked by looking at console messages, however this may be broken or just not work in all cases, because https://amiunique.org/fp does not report them but https://ritter.vg/misc/ff/font-jetbrains.html does, except if you reload. So this is one thing that will need to be investigated. Another thing is Bug 1826418

Comment 1

[Martin Balfanz [:mbalfanz]]

This matches my understanding and sounds overall good to me.
We may tweak the number a bit in the future, but it seems like a good starting point assuming ReportBlockedFontFamilyName reports correctly. In my local testing, the amount of blocked fonts doesn't match the number of messages in the console (e.g. on AmIUnique, on my system I only get 17 out of 21 blocked fonts reported in the console)