Well i dont think there is any way to stop them , i may wrong . But there is also an option named Recently Closed Tabs through which you can see those tabs which were opened by your children .

Block and unblock websites with parental controls on Firefox can help, honestly invest in a third-party content monitoring system.

Also I found this amazing addon that disables history deletion and private browsing. It can be downloaded from here.

It can still be disabled from the add-on manager by anyone, so you need to install this addon and password protect your addons manager and about:config settings.

Block and unblock websites with parental controls on Firefox can help, honestly invest in a third-party content monitoring system.

Also I found this amazing addon that disables history deletion and private browsing. It can be downloaded from here.

It can still be disabled from the add-on manager by anyone, so you need to install this addon and password protect your addons manager and about:config settings.

If your computer has a password system, use it. If the computer can have more than one user account, set one up for yourself (with password), and set up another account for your son. What ever he does on his account should have no effect on you.

There are many programs, most of them are free, that can block adult web sites from your computer. Also, there are programs that can record what he is doing and where. Use a web search for more information.