macOS Sierra. Safari 10.0. App is hanging while loading site or switching tabs
Seems like this an issue with digicert's OCSP and Роскомнадзор. macOS tries to check certificate revocation every time when you change Safari tab with digicert certificate, but IP address is blocked by provider. Same issue with App Store downloads.

I've added different IP address to the /etc/hosts:

72.21.91.29 ocsp.digicert.com

and everything works fine for me now.

Also you can try other solutions or check details from https://stackoverflow.com/questions/39899002/github-is-painfully-slow-on-safari-macos-sierra-10-12