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I was playing around with firewalls and iptables. When I blocked any traffic except HTTP and DNS I was able to establish a connection to via wget But I wasn't able to open via Firefox.

After a little research I found out that Firefox uses the loopback device to communicate with itself (Firefox loopback connection). After I added ACCEPT rules for INPUT and OUTPUT traffic for the loop device, I could open any website via Firefox.

My question is: What exactly does Firefox need the loopback device for?

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I seem to remember it had something to do with parental control. But I'm not sure. – user2428118 Nov 15 '12 at 12:59
There is some more information on this topic here. – rindeal Jan 30 '15 at 2:38

I don't know the details, but believe it has something to do with how it implements the Search Bar with possibly multiple search engines as well as it's ability to provide popular search suggestions as you type.

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