UnMHT outdoes IE Rated 5 out of 5 stars
UnMHT does a much better job writing MHT files than Microsoft's own IE does. As an example, IE can't write an mht of support.microsoft.com/kb/xxxxxx. UnMHT handles the job just fine, and IE has no problem processing the file.
On several occasions I've encountered problems writing MHT files in IE, but unmht is up to the task.
Firefox has no problem reading the files with the extension loaded.