Porn Blocker For Mac
Pop Blocker Mac
On my windows and linux setups I use a hosts file which will block a listed group of websites in all browsers (I use them all for different reasons/checking website design compatibility). Looked for and found a Mac version of a hosts file manager (I don't use Mac so I'm not able to check it comparable to HostsMan which I use on Windows and then copy the file for use on Linux) but it might be the solution you're seeking. MVPS Hosts, which from the site's comments Gas Mask uses, will supply you with ad-blocking and porn/malicious site blocking on any browser on the machine.