What's the best way to filter web content on my computer?

I occasionally let a few other people use my computer, and I want to make sure they aren’t using it to view adult content. Is there a program or extension for Google Chrome I can install to track/monitor/block web content?

I searched through a bunch of Google Chrome extensions, but couldn’t find anything. I also tried OpenDNS, but had some problems adding a network and couldn’t really figure it out.

I’ve also created a guest account and enabled the parental controls so it will keep track of websites visited and try to limit adult content. If there are easier ways to do this on Firefox or Safari then I could only allow the guest account to access one of those instead of Google Chrome.