How do you display SSRS output in just HTML not MHTML - MHTML does not shows up right in browsers other than IE.
In terms of just displaying the report in HTML, you can do the following from a URL perspective:
http://localhost/ReportServer?%2fHelloWorld&rs:Command=Render&rs:Format=HTML4.0&rc:toolbar=false
From an export perspective, you can enable the HTML Renderer to be available for export by modifying the rsreportserver.config file. Just change the visible property to true under the Render extensions.
It will then be an option to export as opposed to MHTML. However, if you are using images or other content, it may not be present in the export.