Files ending in DOCMHTML are MIME HTML files created by earlier versions of Microsoft Word. Among other things, these files contain HTML source code similar to an html file. The source code is created in such a way that the browser displays a doc or docx document as similar as possible to Word. Docmhtml files may also contain other resources such as images or audio files.
The DOCMHTML format is no longer supported by Microsoft. Documents that should be published on the Web should therefore be saved as an mhtml or mht file.
Newer versions of Microsoft Word save HTML code as an html file.
Mozilla Firefox needs to display a MHT plugin.