XML Sitemap files are invalid

[a-kyne]

Summary Although the Sitemap index file is valid ( https://developer.mozilla.org/sitemap.xml), none of the three XML files it links to are valid.

Steps To Reproduce (STR)

1. Visit the following URLs:

• https://developer.mozilla.org/sitemaps/fr/sitemap.xml.gz
• https://developer.mozilla.org/sitemaps/en-us/sitemap.xml.gz
• https://developer.mozilla.org/sitemaps/ja/sitemap.xml.gz

2. Attempt to open the files.

Actual behavior File does not open as XML. "Encoding error"

Expected behavior I should be able to open the files and validate the XML.

Additional context