Doubling of content in Firefox

I have to document this since I have had come across this 3x so far, each time a week apart so I forget what I did to fix it.  We are using tinymce in drupal, and when the content is rendered in firefox, it will be displayed 10 times. 
The root cause of the problem was that there was an html comment present in the content.  Since the html comment is escaped out (yes, I am using full html), this messes up the page in firefox. 
Removing the html comment fixed it.
Update (a week later).  Ran into this problem again on firefox.  There was NO html comments.  The problem was that there was a double dash (--) in the content.  Once I removed this, or replaced it with a "—", all was well