There are generally two types of webpages on the Internet; those that are static and those that are created dynamically when a user points a web browser to a website. Either way, Firefox and other web browsers treat all webpages as if they are files.
As files, webpages have certain attributes that make them accessible to the web browser. For example, webpages have a file size, data of publication, encoding and rendering modes, and even a list of security information provided by the owner of the website. Using the Page Info feature in Firefox, you can examine all of this information about a webpage.