Safari not loading pages, other browsers doing fine
By verifying the issue in the Guest user you have identified the issue resides in a system shared resource.
Attempt to reproduce the issue in Safe Mode. If the issue is not reproducible, reboot normally and check if the issues persist. If it does I would encourage you to backup your system and navigate over to the local Library located at /Library. From here you can start troubleshooting by removing files from locations such as:


./StartupItems
./LaunchAgents
./LaunchDaemons
./Internet Plug-ins


Reboot your system and attempt to reproduce after each change. If all else fails you may be looking at an erase and install of your OS and selective migrating your data back on to the drive to avoid migrating the issue over.

Hope this helps!