What page(s) did you find the problem on?

• files/en-us/learn/html/introduction_to_html/the_head_metadata_in_html/index.html
• files/en-us/web/css/background-repeat/index.html
• files/en-us/web/html/element/menuitem/index.html
• files/en-us/web/http/basics_of_http/evolution_of_http/index.html
• files/en-us/web/http/headers/host/index.html

What is the problem?

developer.cdn.mozilla.net and its backing CDN will be de-commissioned.

What did you expect to see?

All references to developer.cdn.mozilla.net should be replaced with developer.mozilla.org.