1977576 - PDF has started rendering blank with fingerprinting protection due to new WebCodecs RFPTarget

Status: VERIFIED FIXED

(Core :: Privacy: Anti-Tracking, defect, P3)

Description

[Kestrel]

Attachment: PDF renders blank with FPP and WebCodecs RFPTarget enabled

STR:

1. Enable fingerprinting protection (FPP) with all RFPTargets enabled on latest Nightly 142.0a1:
   privacy.fingerprintingProtection = true
privacy.fingerprintingProtection.overrides = +AllTargets
2. Open PDF: https://pigeoncote.com/books/pp/pp13index.pdf.

Expected:
PDF fully renders.

Actual:
PDF is blank except for watermark on bottom.

Works with:
privacy.fingerprintingProtection.overrides = +AllTargets,-WebCodecs

Fails with:
privacy.fingerprintingProtection.overrides = -AllTargets,+WebCodecs

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=e509c680c3b146dd3f0827ec267f81976a8e5104&tochange=a86c4baa7bc5f4daf3950e589126d765df298eed

Regressed by Bug 1973265.

Comment 1

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

:fkilic, since you are the author of the regressor, bug 1973265, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 2

[Fatih Kilic [:fkilic]]

Unfortunately our pdf.js detection is broken, so we fail to exempt it. I'm honestly not sure what can be done about this. I have tried fixing the pdf.js detection in the past but failed. I have something in mind and I'll try that, but I'm not 100% sure if it'll work. I'll send a patch if it works, if it doesn't i'll report back here.

Comment 3

[Fatih Kilic [:fkilic]]

interesting not all pdfs are affected. maybe there's some conditional thing

edit: i just noticed even in the sample pdf some things are rendered.

Comment 4

[Fatih Kilic [:fkilic]]

Attachment: Bug 1977576 - Pass JSContext to VideoFrame::PrefEnabled in more places. r?manuel

Comment 5

[Fatih Kilic [:fkilic]]

the issue seems to the be structured clone failing with postMessage. We don't pass JSContext to VideoFrame::PrefEnabled causing it to not check for pdfjs exemption. So, the attached patch should fix it by passing JSContext to VideoFrame::PrefEnabled.

Comment 6

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

Set release status flags based on info from the regressing bug 1973265

Comment 7

[Dianna Smith [:diannaS]]

:fkilic can you set a priority/severity for this? wondering if we are still targeting 142 here

Comment 8

[Fatih Kilic [:fkilic]]

Assuming this only affects RFP and the regression wasn't included in 140ESR (Tor Browser uses ESR and TB uses RFP), I don't think we need to target 142.

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/385990abc503
https://hg.mozilla.org/integration/autoland/rev/27e458b93006
Pass JSContext to VideoFrame::PrefEnabled in more places. r=manuel,chunmin,tjr

Comment 10

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/27e458b93006

Comment 11

[Monica Chiorean]

I was able to reproduce the issue on Win11x64 using FF build a1(20250709215737).
Verified as fixed on Win11x64 using FF build 144.0a1(20250825091413) and 143.0b3.