testcafe: 'TypeError: this.res.setHeader is not a function' error appears, when specified 'http://localhost:3000' page url (Firefox only)

Are you requesting a feature or reporting a bug?

Bug

What is the current behavior?

FF window is opened, navigation on url is done, failing occurs on next line after navigation, testCafe stops execution.

What is the expected behavior?

TestCafe should continue tests execution

How would you reproduce the current behavior (if this is a bug)?

1. Install latest testCafe version.
2. Install latest FF version.
3. Trigger tests execution in FF.: testcafe.js firefox ./{somePathToTests} s -r spec,nunit:./${somePathToResults} -e --selector-timeout 2000

Provide the test code and the tested page URL (if applicable)

Tested page URL: http://localhost:3000

Test code:

Specify your

• operating system: Mac OS X 10.12.0
• testcafe version: 0.20.0, 0.19.2
• node.js version: v8.9.4