That would be a question for McAfee support.

From the problems I have seen posted in this forum over the years about "cleaning programs" breaking Firefox or not working as expected, you are better off not allowing external programs like that to "clean" any Firefox data files. Too many times the internal Firefox data files get corrupted or broken by external programs, probably because the programmers for those external programs don't really know how the Firefox data files work (most are sqlite database files now-a-days) or their application wasn't tested well enough, like with many of the most common extensions installed.

IMHO, if you want to "clean" Firefox use what is built into Firefox already, and don't use external applications to do that "cleaning".
https://support.mozilla.com/en-US/kb/Clear%20Recent%20History

McAfee support told me that it only works with IE. They said that Firefox will be added to future versions... Thanks for the advice and info!