Cross-Origin Request Blocked warning messages when set to any external network

[filippsen]

Browser

Firefox

Description

When set to any external network, undeployed or deployed contract results into infinite set of Cross-Origin Request Blocked messages.

Steps to reproduce

1. From Hello World template
2. Set network to Ropsten

Expected result

No warnings.

Actual result

After switching to external network, the following warning message shows in browser console:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://ropsten.infura.io/v3/[...]. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing).

This is not strictly related to undeployed contracts or the Preview window.