1619349 - Add telemetry to determine potential impact of anti-font-fingerprinting measures

Status: RESOLVED FIXED

(Core :: Layout: Text and Fonts, enhancement, P3)

Description

[Jonathan Kew [:jfkthame]]

We are considering measures to limit font-based fingerprinting by restricting the set of fonts that are exposed via CSS font-family etc.

To better understand the potential impact of such changes, we should add telemetry to find out how frequently users may see rendering differences or breakage.

I propose that as an initial step, we should report:

• How often does a page fail to find any font, and resort to hexbox rendering?
  • If the frequency of this rises noticeably when we make changes, that would suggest users are getting a bad experience
• How often does a page use a locally-installed font that was not part of the default (OS-provided) font collection?
  • These are fonts that we are considering blocking, which means the rendering of the page would change
• How often does font fallback end up using a non-OS-provided font?

We already have some webfont telemetry in place; this is probably a reasonable place to add installed-font telemetry as well.

Comment 1

[Jonathan Kew [:jfkthame]]

Attachment: data-review request

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1619349 - patch 1 - Record statistics about font-matching behavior in the presContext. r=jwatt

Depends on D66125

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1619349 - patch 2 - Report font-matching statistics via telemetry ping. r=chutten

Depends on D67787

Comment 4

[Chris H-C :chutten]

Comment on attachment 9133672 [details]
data-review request

DATA COLLECTION REVIEW RESPONSE:

    Is there or will there be documentation that describes the schema for the ultimate data set available publicly, complete and accurate?

Yes. This collection is Telemetry so is documented in its definitions file [Histograms.json](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/telemetry/Histograms.json) and the [Probe Dictionary](https://telemetry.mozilla.org/probe-dictionary/).

    Is there a control mechanism that allows the user to turn the data collection on and off?

Yes. This collection is Telemetry so can be controlled through Firefox's Preferences.

    If the request is for permanent data collection, is there someone who will monitor the data over time?

No. This collection will expire in Firefox 82.

    Using the category system of data types on the Mozilla wiki, what collection type of data do the requested measurements fall under?

Category 1, Technical.

    Is the data collection request for default-on or default-off?

Default on for all channels.

    Does the instrumentation include the addition of any new identifiers?

No.

    Is the data collection covered by the existing Firefox privacy notice?

Yes.

    Does there need to be a check-in in the future to determine whether to renew the data?

Yes. :jfkthame is responsible for renewing or removing the collection before it expires in Firefox 82.

---
Result: datareview+

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/f8ca02252dfc
patch 1 - Record statistics about font-matching behavior in the presContext. r=jwatt
https://hg.mozilla.org/integration/autoland/rev/ba16b09b5da0
patch 2 - Report font-matching statistics via telemetry ping. r=chutten

Comment 6

[Andrei Ciure[:aciure]]

Backed out 4 changesets (bug 1619349, bug 1619350) for causing test_font_whitelist.html to fail
https://hg.mozilla.org/integration/autoland/rev/6f834ef903846d598280d3d1274d626a92bfe863

push that caused the backout: https://treeherder.mozilla.org/#/jobs?repo=autoland&searchStr=os%2Cx%2C10.14%2Cshippable%2Copt%2Cmochitests%2Ctest-macosx1014-64-shippable%2Fopt-mochitest-plain-e10s-3%2Cm%283%29&fromchange=ba16b09b5da09481992160919cf6a4c2329db6cd&tochange=87b08f234fe825a7da949ce2a76b64d3071c235f

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/62f8ce89dce8
patch 1 - Record statistics about font-matching behavior in the presContext. r=jwatt
https://hg.mozilla.org/integration/autoland/rev/1a8269aa3f6e
patch 2 - Report font-matching statistics via telemetry ping. r=chutten

Comment 8

[Stefan Hindli [:stefan_hindli]]

https://hg.mozilla.org/mozilla-central/rev/62f8ce89dce8
https://hg.mozilla.org/mozilla-central/rev/1a8269aa3f6e