MHTML
Short for MIME Encapsulation of Aggregate Documents, such as HTML, MHTML is a file format that stores the entire contents of a web page in a single file (.mht or .mhtml). For example, this HTML (hypertext markup language) web page, its CSS (cascading style sheets), and images could be saved in a single file called "example.mht," and easily shared and opened by other people.
The MHTML file format was proposed in RFC 2557 in March 1999 and was first available with Internet Explorer 5.0. Since then, it's been natively supported in versions of Chrome, Edge, Opera, Vivaldi, and Yandex. Other browsers, like Firefox and Safari, that do not natively support MHTML can use an add-on for MHTML support.
In addition to browser support, programs like the Steps Recorder also use this format when creating content to share.
How to open an mht file in Edge
With Windows 11, Microsoft removed Internet Explorer, which was required for MHTML files. To open these files in Edge, IE mode (Internet Explorer mode) must be enabled.