Firefox doesn't use the built-in certificate store like everybody else. They have their own.
1) Go to options
2) Security
3) View certificates

4) Go to the Authorities tab
5) Click the "Import Button"
6) Browse to where you stored the Cato Root Certificate and select it.

That should clear up constant certificate issues with TLS inspection under Firefox.

For more general cases, see 

115000443145-How-to-install-Cato-s-certificate