Poster

A developer tool for interacting with web services and other web resources that lets you make HTTP requests, set the entity body, and content type. This allows you to interact with web services and inspect the results...

https://addons.mozilla.org/fr/firefox/addon/2691/

HTTP Resource Test

This simple addon allows you to see the raw output from an HTTP server in response to a request. You can send requests using any standard HTTP method. POST and PUT requests allow you to send an entity with the request. You can also set the HTTP Accept header.

https://addons.mozilla.org/z/en-US/firefox/addon/15045/