I'm using OpenVPN to tunnel traffic for end users. Recently I've had a similar problem on multiple servers with connecting to several webpages. When I disconnect from the VPN every website works fine, but when I turn the VPN on there are a few websites (that I know of) that work incorrectly. Meaning that I can't always open up features on the site (or ping the site in the case of mozilla.org). Typically login popups and other windows are the features that won't work. Additionally I can't connect to mozilla.org at all. I've updated everything client side. The servers have not been touched since the initial installation both of which are 12+ months in the past. This problem has popped up around 2 weeks ago and I can't figure out what is causing the error for my users.