MDN documentation linter per MDN

A Firefox add-on that creates a sidebar that appears while you're editing on MDN, providing some tools for testing and validating your content.

This WebExtension is useful for MDN contributors who want to help cleaning up MDN pages. A few test highlights:

- Tests if macro / template calls are valid (e.g. things like {{HTMLElement("abbr")}}).
- It informs you about the article length, and warns you when creating way too long pages.
- It informs you whether you've added style attributes, or span, font, or other HTML soup elements into the page.
- It warns you when you didn't add a syntax highlighting class to code examples
- ... and many more!

The MDN documentation linter is a project of the MDN team (https://developer.mozilla.org) and you can help improving it on GitHub https://github.com/mdn/doc-linter-webextension