More findings about Firefox:
1. Download firefox from mozilla.org
2. firefox --ProfileManager --no-remote
3. Create a new profile and choose "Work offline"
4. Click "Start Firefox"
So far: zero packets sent
5. Close firefox
Result:
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
212
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
212
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
126
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
126
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
418
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
415
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
2896
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
1223
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp
2032
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 31
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 31
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59810 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
IP pc.59812 > ec2-52-38-149-111.us-west-2.compute.amazonaws.com.https: tcp 0
Obviously that is "Work Offline" according to Mozilla.
