To be more specific, the title should be "Add image/webp to default Accept
navigation header"
That is, include image/webp when content policy is DOCUMENT/SUB_DOCUMENT.

fetch()/"Save as" is with `Accept: */*" as is.

Thanks for any feedback.

On Thu, Oct 31, 2019 at 4:31 PM Junior Hsu <> wrote:

> Summary:
> I'd like to increase the visibility for this controversial intention.
> Currently Firefox send
> image/webp for image content, but it fails for navigation case. By adding
> image/webp
> to default Accept:, developers can tell the webp support by Accept header
> for navigation
> and opening URL by other application, other than inspect if version >= 65
> by User-Agent.
> However, it doesn't not align the spec, and it makes the Accept: longer in
> a hack way.
> FWIW, we add image/webp to default Accept header in 65, and it's removed
> in 66 for
> aligning the spec.
> Please see the detailed discussion in the following bug, and feel free to
> weigh in here
> or on the bug.
> Bug:
> Link to standard:
> 4.1.3
> Platform coverage: This will be exposed to all platforms.
> Estimated or target release: Firefox 72
> Do other browser engines implement this? Chrome, who supports webp, did.
> Is this feature enabled by default in sandboxed iframes? Yes.
> Junior
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