UPDATE:
Might want to ignore above posts. A waste of time. Mint 13 is riddled with bugs. Example:Can't used suspend,freezes and locks up. If your computer can handle it, stick with Mint 17. I'm stuck with Mint 13 on a old machine with bugs but way better than Lubuntu 14.04LTS and Peppermint 3. They come with more numerous irritating bugs.
From:
Google search:
https://www.google.com/search?q=mime...m=122&ie=UTF-8
"Bug Description---one of many.
No applications found in file manager preferences
https://bugs.launchpad.net/bugs/1016956
Launchpad
Jun 23, 2012 - ... to .local/share/applications/mimeapps.list makes no difference Release 13 Maya with Mate DE. ... Linux Mint Edit. New. Undecided.
This bug affects 3 people
From:
http://www.cesareriva.com/category/mint-mate/
Linux Mint Mate: MIME settings reset
I am running Linux Mint Mate 13 Maya, to reset the personal MIME settings type just delete this file:
rm ~/.local/share/applications/mimeapps.list " ---------------------Bad advice?
Here is the solution: If newbie, leave Firefox/Tomboy/Mint 13 mate this alone. Do not do anything and live with it. I read through the above Google search and found two more different associated bug reports numbers, some dating around 2004. Seems to be a conflict between Mint 13 mate with Caja and a bond with Firefox. Big Hair Ball.
Will mark as (SOLVED).