XQuartz is causing Internet connection problems

I too wanted to install Inkscape, so I first installed Xquartz on my Macbook Pro (OS: El Capitan). Everything appeared to be fine. Inkscape opened and was usable. However, the following day (today), I found that I can use Chrome, but Safari and Firefox cannot access web pages. I can open iTunes software, but I cannot access the iTunes Store; I can open Skype but cannot make calls; I can open the App Store software, but I cannot access the App Store, and I cannot connect to my website's server with FileZilla. I can, however, download files from Dropbox, use GIMP, Pages (Apple software), Word, VLC, and Inkspot. Norton is operating fine and turning off its firewall does not help the other issues.

On http://xquartz.macosforge.org/trac/wiki/X112.7.8 website, it says:

D Default X11 Serverhttp://xquartz.macosforge.org/trac/wiki/X112.7.8#DefaultX11Server

If this is your first time installing XQuartz, you may wish to logout and log back in. This will update your DISPLAY environment variable to point to XQuartz.app rather than X11.app. If you would prefer to keep using X11.app as your default server (you can still launch XQuartz.app manually), you'll want to disable /Library/LaunchAgents/org.macosforge.xquartz.startx.plist using ​launchctl(1).

If I applied this redirect, would my computer be functional again?

Any ideas on how to fix this would be welcome. Alternatively, if anyone can point me to some instructions to uninstall Xquartz completely, I would appreciate that too.