BlockSite - BlockSite is an extension, which automagically blocks websites of your choice.
E2Guardian - Web filtering solution
FocusMe - With so much access to information and distractions on the internet, it's easy to get sidetracked.
NxFilter - Best performance. You don't want to slow down your network by installing a network security software. NxFilter is a light-weight DNS filter. It doesn't cause any latency issue in your network.
Stay Focused - More suitable with Google Chrome, this service enables you ensure you do not waste precious time on updating Facebook status or chatting with people.
Qustodio - Free parental control software. Monitor and track your child's online activity. Block dangerous sites and protect kids from online bullying.