Go to about:config. In the filter, enter network.http.version and a single entry comes up to tell you the version. You can change it if you want.
HTTP functions as a request-response protocol in the client-server computing model. In HTTP, a web browser, for example, acts as a client, while an application running on a computer hosting a website functions as a server. The client submits an HTTP request message to the server. The server, which stores content, or provides resources, such as HTML files, or performs other functions on behalf of the client, returns a response message to the client. A response contains completion status information about the request and may contain any content requested by the client in its message body.
The aim of HTTP protocol is to allow transfer of files (essentially in HTML format) between a browser (the client) and a Web server (called among other things httpd on UNIX machines) located using a character string called a URL.