There is only one file type that uses the .MOBIRISE extension:
Mobirise Project File
A MOBIRISE file is a project created by Mobirise, a free Windows, macOS, and Android program that allows users to build websites without any coding. It contains "blocks" that make up the site, which may include a menu, header, articles, images, videos, sliders, galleries, features, pricing tables, forms, tables, and footers. MOBIRISE files are saved in JSON format.
project.mobirise - Default name given to a project saved by Mobirise.
Updated: July 30, 2018