Chrome and FF

Looking at Norton for famly security and want to start by putting my vote in for Chrome.  

 

Finding a lot of inconsistentcies though in blocking sites with FF.   Sometimes I can login, start FF and get to google.com and sometimes it is blocked.   Sometimes after it is blocked I can still get to it by typing in odd search phrases in FF search bar.  For example typing in 'thong' will get blocked but typing in 'skindex' (a website that creates minecraft skins) allows you thru to google.. at which point I can type in thong and see all kinds of stuff I dont want my kids to see.

 

I have turned off MS family filtering and I use Avast and have disabled the web and other real time monitoring as a test.   

 

Any thoughts why sometimes it will block a site but other times let it thru?