# Page Not Found

The URL `add-ons/mailextensions/hello-world-add-on/using-webextension-apis` does not exist.

You might be looking for one of these pages:
- [Using WebExtension APIs](https://developer.thunderbird.net/add-ons/hello-world-add-on/using-webextension-apis.md)
- [Supported WebExtension APIs](https://developer.thunderbird.net/add-ons/mailextensions/supported-webextension-api.md)
- [Using Content Scripts](https://developer.thunderbird.net/add-ons/hello-world-add-on/using-content-scripts.md)
- [A Guide to Extensions](https://developer.thunderbird.net/add-ons/mailextensions.md)
- [Using a Background Page](https://developer.thunderbird.net/add-ons/hello-world-add-on/using-a-background-page.md)

## How to find the correct page

1. **Browse the full index**: [/sitemap.md](https://developer.thunderbird.net/sitemap.md) - Complete documentation index
2. **View the full content**: [/llms-full.txt](https://developer.thunderbird.net/llms-full.txt) - Full content export

## Tips for requesting documentation

- For markdown responses, append `.md` to URLs (e.g., `/add-ons/hello-world-add-on/using-webextension-apis.md`)
- Use `Accept: text/markdown` header for content negotiation