Check for blocking add-ons or child protection programs. Also, check your other protection programs.

Are you getting any messages? Are you going to sites via search engines? No need for details, but are the sites ones your mother might have censored? Search engines like Google have settings that can enable or disable "safe" searching.

Firefox does have some built in protection and if you see messages from that it may be wise to take heed of them

• How does built-in Phishing and Malware Protection work?

Or maybe you are seeing security warnings such as these

• What do the security warning codes mean?
• How to troubleshoot security error codes on secure websites