Intent to prototype: prefers-reduced-transparency media query

[Oj]

Summary:

The "prefers-reduced-transparency" media query allows websites to reduce the amount of transparent objects/effects to become more accessible for some users who may have difficulties parsing content through translucent backgrounds, etc. Based on system settings.

With https://phabricator.services.mozilla.com/D172424, it is now implemented behind the preference said below, disabled by default.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1736914

Specification: https://www.w3.org/TR/mediaqueries-5/#descdef-media-prefers-reduced-transparency

Standards body: W3C

Platform coverage: All

Preference: layout.css.prefers-reduced-transparency.enabled

DevTools bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1822185 for emulation
Standards position: https://github.com/mozilla/standards-positions/issues/393

Other browsers:

- Blink: Not shipped or implemented. No bug or standards position.

- WebKit: Not shipped or implemented. Bug: https://bugs.webkit.org/show_bug.cgi?id=175497. Specific standards position: https://github.com/WebKit/standards-positions/issues/145

Web platform tests: Added in same Gecko patch, https://phabricator.services.mozilla.com/D172424

How stable is the spec: Media Queries Level 5 is currently a Working Draft.

Security & privacy concerns: This potentially introduces a fingerprinting vector, so the pref for this specific media query will be kept disabled by default until decided. Bug for potentially enabling by default: https://bugzilla.mozilla.org/show_bug.cgi?id=1822176

Web designer / developer use-cases: Some users find it hard to parse text or content with translucent backgrounds. This media query can allow websites to make pages more opaque to assist people who may struggle otherwise.

[Henri Sivonen]

On Mon, Mar 13, 2023 at 11:36 PM Oj <o...@oojmed.com> wrote:

Summary:

The "prefers-reduced-transparency" media query allows websites to reduce the amount of transparent objects/effects to become more accessible for some users who may have difficulties parsing content through translucent backgrounds, etc. Based on system settings.

I added a comment to the standards-position issue recounting how, anecdotally, people (including me) have ended up with this pref set on Mac for reasons that don't involve an essential a11y need:

https://github.com/mozilla/standards-positions/issues/393#issuecomment-1469972067

I think exposing a bit of fingerprinting entropy is problematic especially given how/why people end up with this pref set on Mac.

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Henri Sivonen
hsiv...@mozilla.com