Simon Asks about locking down Firefox

Simon writes...

I'm not an IT professional but often the person in family and friends circle who's called if the computer doesn't work.
On several occasion I saw Firefox installs (on Windows and Linux) with adware/malware extension installed that hijack search and links.

My question to you and the community: Is there a way to disallow adding extensions by the user except a white list of extension I added during setup of the system? While the user still owns .config/app profile files or a big config management system.