Custom Headers от Anto

Custom Headers lets you override or add HTTP headers on the browser's requests and responses.
Features
- Two separate sections: Request Headers and Response Headers.
- Add or remove header rows on the fly (name + value).
- Enable/disable toggle on every row.
- Optional per-row "URL match pattern" to limit a rule to specific sites (default: all URLs).
- Smart behaviour: if a header already exists, its value is replaced; otherwise it is added.
- Rules are stored locally and persist across browser restarts.
- Clean, minimal popup, localized in 12 languages.

Privacy
The extension does not collect, store remotely, or transmit any data. Every rule stays in your browser's local storage. Built entirely on the standard declarativeNetRequest API, with no external dependencies.
Open source (MPL-2.0): https://gitlab.com/mrdjtoto/mozilla-custom-headers