Knowing that, and tracking down the relevant config entries, I created a "user.js" file with the following content and pushed it into the Firefox profile directory for the target (in this case public) user, and it turned the settings off for them without having to mess with the UI at all.
I will be blasting this user.js file out to all of our public desktops later today.
On Windows this goes into the user's appdata/Roaming/Mozilla/Profiles/"profile name" directory
This is probably only useful if you have to do it on a mass scale (otherwise, just use the UI). It's going to be a huge timesaver for me, and hopefully a few others though.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko