mdn/content

Mention Firefox Anti-fingerprinting on `getImageData()` page

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#39,084 opened on Apr 11, 2025

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Content:WebAPIhelp wanted

Description

MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/getImageData

What specific section or headline is this issue about?

No response

What information was incorrect, unhelpful, or incomplete?

The page for CanvasRenderingContext2D.getImageData() does not mention that the result may be influenced by anti-fingerprinting, e.g. Firefox's protection against fingerprinting:

Random data is introduced to background images when the image is read back by the website. If a website merely renders data to the background, it will render without alteration. Although typically this does not happen, if the website reads the image data in the background (and potentially displays it to you again), it will have subtle noise that may affect how the image is displayed.

What did you expect to see?

It would be useful for web developers that use this feature, to mention this potential impact of anti-fingerprinting on the page.

Do you have any supporting links, references, or citations?

This was originally reported in this BCD issue.

Do you have anything more you want to share?

No response

MDN metadata

Contributor guide

Tech stack
javascripthtmlcss
Domain
documentation
Issue type
documentation
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic knowledge of canvas APIfamiliarity with anti fingerprinting concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
90
Research direction
The issue requests adding a note about Firefox's anti fingerprinting affecting getImageData() results. See the existing MDN page at files/en us/web/api/canvasrenderingcontext2d/getimagedata/index.md. Reference the linked BCD issue for more context. The fix is localized: add a brief paragraph after the description, possibly with a note box, linking to the Firefox anti fingerprinting support page. No code changes are needed, only documentation.