hosts file settings:

- to deploy to Heroku

  174.129.22.147 git.heroku.com

- to enable Twitter from Web

  104.244.42.65 twitter.com
  93.184.220.70 pbs.twimg.com
  104.244.43.7 o.twimg.com

- to access Github (as another poster wrote):

  192.30.253.113 github.com
  151.101.4.133 assets-cdn.github.com

You can find any other IPs you need on sites like http://www.hcidata.info/host2ip.cgi

Just remember to rollback your hosts file after the outage finishes.