Hi

Which adult content filter are you trying to disable?

This does not sound like an issue with Firefox, but is something that your internet service provider may be able to help you with.

Such can be blocked by, 1) Adult blocking add-ons 2) Adult blocking filters/programs on the system

How do I get rid of "adult blocking add-ons?" Where is it on my computer? Same questions about "adult blocking system"

If it is not a filter that you have installed yourself on your device, it will be something that your internet service provider should be able to help you with.