Installing, configuring proxies can do what you are complaining about. Go back to stock and it should clear up.
If you have a proxy issue, take that up with the proxy support site/forum.
Bob
I have a Macbook Pro and just recently, I haven't been able to log into Facebook with any of my browsers (Firefox, Safari, Google Chrome). It says pretty much the same thing for all of them - that the secure connection failed or some error occured. This is also happening for other websites like Amazon (especially when I use a proxy like AnonymoX). These are big websites, so it is rather confusing to me
Does anyone know how I can fix this?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic