Missing CSS on some pages at MDN

On the https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver URL, I see it as unstyled content. This was working some days ago.

imagen

This happens only using Firefox. Using Brave it looks fine.

Inspecting the request, I see a request for this URL that returns a 404 error:

https://developer.mozilla.org/static/css/main.a43ed10c.chunk.css

Surprisingly, on Brave it returns a 200 response.

I've managed to reproduce the issue with cURL, and the difference is the Accept-Language header.

:~> curl -s -D - -o /dev/null https://developer.mozilla.org/static/css/main.a43ed10c.chunk.css
HTTP/2 200 
content-type: text/css; charset=utf-8
content-length: 53328
date: Tue, 28 Sep 2021 08:19:03 GMT
cache-control: max-age=31536000, public
last-modified: Tue, 28 Sep 2021 01:43:00 GMT
etag: "60c05bad31eb459142ffac4899eb11f1"
server: AmazonS3
x-frame-options: DENY
x-xss-protection: 1; mode=block
x-content-type-options: nosniff
strict-transport-security: max-age=63072000
vary: Accept-Encoding
x-cache: Hit from cloudfront
via: 1.1 911151077fc74374130cb3f3f2d671e8.cloudfront.net (CloudFront)
x-amz-cf-pop: MAD51-C2
x-amz-cf-id: _WolSYWZTsBfSh3dpWTDOeH7SrfaS_gk_3hOLDfhg4hA5NMc25nqmg==
age: 3762039

:~> curl -s -D - -o /dev/null -H 'Accept-Language: es' https://developer.mozilla.org/static/css/main.a43ed10c.chunk.css
HTTP/2 404 
content-type: text/html; charset=utf-8
content-length: 22626
date: Wed, 10 Nov 2021 21:24:03 GMT
cache-control: no-store, must-revalidate
last-modified: Wed, 10 Nov 2021 02:00:15 GMT
etag: "14ed81a73921f780157b1a4567ce600a"
server: AmazonS3
x-frame-options: DENY
x-xss-protection: 1; mode=block
x-content-type-options: nosniff
strict-transport-security: max-age=63072000
content-security-policy: default-src 'self'; script-src 'report-sample' 'self' *.speedcurve.com 'sha256-q7cJjDqNO2e1L5UltvJ1LhvnYN7yJXgGO7b6h9xkL1o=' www.google-analytics.com/analytics.js 'sha256-JEt9Nmc3BP88wxuTZm9aKNu87vEgGmKW1zzy/vb1KPs=' polyfill.io/v3/polyfill.min.js assets.codepen.io production-assets.codepen.io; script-src-elem 'report-sample' 'self' *.speedcurve.com 'sha256-q7cJjDqNO2e1L5UltvJ1LhvnYN7yJXgGO7b6h9xkL1o=' www.google-analytics.com/analytics.js 'sha256-JEt9Nmc3BP88wxuTZm9aKNu87vEgGmKW1zzy/vb1KPs=' polyfill.io/v3/polyfill.min.js assets.codepen.io production-assets.codepen.io; style-src 'report-sample' 'self' 'unsafe-inline'; object-src 'none'; base-uri 'self'; connect-src 'self' www.google-analytics.com stats.g.doubleclick.net; font-src 'self'; frame-src 'self' interactive-examples.mdn.mozilla.net mdn.github.io yari-demos.prod.mdn.mozit.cloud mdn.mozillademos.org yari-demos.stage.mdn.mozit.cloud jsfiddle.net www.youtube-nocookie.com codepen.io; img-src 'self' *.githubusercontent.com *.googleusercontent.com lux.speedcurve.com mdn.mozillademos.org media.prod.mdn.mozit.cloud media.stage.mdn.mozit.cloud interactive-examples.mdn.mozilla.net wikipedia.org www.google-analytics.com www.gstatic.com; manifest-src 'self'; media-src 'self' archive.org videos.cdn.mozilla.net; worker-src 'none';
vary: Accept-Encoding
x-cache: Error from cloudfront
via: 1.1 fcb5d6664fcce90309288d9ff2cfb9a5.cloudfront.net (CloudFront)
x-amz-cf-pop: MAD50-C1
x-amz-cf-id: bFvB5YAmqVPe9cRWCGVxcvv5mi4SblgKKQu4U8wd4YgPdSgVsvInRA==

If this is a caching problem, it will probably clear itself, but I feel like it needed to be reported. Sorry if it is not the right repository or place to report this!

mdn / infra

Missing CSS on some pages at MDN #519