This measure could break some sites. Mozilla feels that it is finally better to keep the users off sites’ radars by default.
If the users run into problems, there is a central control area where they can change their privacy and security settings.
Also, it enforces add-on verification by default so that social plug-in the users downloaded should not add unwanted toolbars, solid material ads or collect more data than it should. The users can turn off this filter.