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

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

• Folder: en-us/web/api/canvasrenderingcontext2d/getimagedata
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/getImageData
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/api/canvasrenderingcontext2d/getimagedata/index.md
• Last commit: https://github.com/mdn/content/commit/e9b6cd1b7fa8612257b72b2a85a96dd7d45c0200
• Document last modified: 2025-04-10T14:56:07.000Z