Go in menu->settings->settings->select the tab "Privacy" and here in History select "Remember history". See also the screenshot

this is already set this way. I need to make it so that the user cannot delete the history if/when they are viewing personal items on company time.

Check it here ..

Click here

You can't disable this in Firefox. There are a lot of ways to delete the history and deleting the places.sqlite file file in the Firefox profile folder will remove all history anyway. You will have to use other means at the OS level if you want a record of visited websites that covers all browser. I would assume that you could even delete the IE history files if you have write access to the location that stores the IE history.