It's a very useful extension for websites.

Add and modify the content of HTTP-request headers for any website. It's very useful for developers who want to change the content of HTTP requests from a website. It also helps them test a website by adding and removing headers for the request.

Add a new header for any request on the desired domains, and modify it's content.

Change the value of the header item.

The header item has many options to modify it's content, or its value.

To install the addon, open the Options page and click "Download and Install".

The extension has an icon in the Add-ons section of the Options page.