Microsoft* Word and Internet Explorer as well as Opera allow to save a Web
page as a single MHTML file, called Web archive. Such an archive
encapsulates all the resources necessary to display a Web page into
a single archive file that can be viewed offline. By default MHTML archives
are not supported by Firefox. The package mhtml-firefox
installs the Firefox extension MHTML Archive Reader
for all users and also binds MHTML archives (ending in either
.mht or .mhtml) to Firefox in the
desktop shell.