[HTML] data: and javascript: not allowed in href

[dipikabh]

Acceptance criteria

• The listed features are documented sufficiently on MDN
• BCD is updated
• Interactive example and data repos are updated if appropriate
• The content has been reviewed as needed

For folks helping with Firefox related documentation

• Set bugs to dev-doc-complete
• Add entry to Firefox release notes for enabled/preview features
• Add/remove entry to Firefox experimental features page for preference/released features

Features to document

Related pull requests:

• HTML base element: data and javascript URLs disallowed #28917
• html base element - forbid href with data or javascript url browser-compat-data#20646

Related Gecko bugs

Bug 1850967: Forbid data: and javascript: URLs in <base>

Other

• Check content open issues to see if any pertain to the subject matter. If there are any that can be closed because of the work, do so. If there are any that can be fixed relatively quickly because of the knowledge from completing this issue and you have time, feel free to go ahead and fix them.

[hamishwillee]

Status

• BCD FF127 base href forbids javascript and data URLs browser-compat-data#23164
  • Updated ^^^ to note versions in which dynamic updates supported
• Docs - OK
  Note, I think fallback URL documented correctly to match spec https://bugzilla.mozilla.org/show_bug.cgi?id=1850967#c8
• Release note FF127Relnote- data: and javascript: URLS forbidden in base HREF #33738
• dev-doc-complete