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On macOS 15.5, Firefox 139 shows super dark images for me. Safari seems to work fine, though.

I'm curious if someone knows what's going on. It feels to me like Firefox is showing the image in HDR but with the wrong gamma curve applied.

MacBook Pro can “display” HDR content on SDR displays.

macOS puts a slightly higher brightness than it required and artificially (in software) changes absolute white (0xFFFFFF) to greyish color (0xEEEEEE). So when a HDR content is required it will remove mask around that content. Safari ideally, probably that’s on Firefox why tone mapping doesn’t work well

There's a HDR video on that page, and on my built-in MBP display, it's much brighter/has noticeably more range than the rest of the UI. Moving the window to my non-HDR external 4k monitor, it looks like a regular YouTube video.

The video looks the same in both Safari and Firefox, whereas the images are dim in Firefox on both my MBP display and external monitor.

Firefox does not have HDR support for images. It has some support for HDR video on Mac. Support for HDR images seems to have gained some traction in latest months but seems still distant.

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

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