UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0

Steps to reproduce the problem:
1. Open the attached page myScreen.html in chrome
2. Go to dev tools and activate the device emulation
3. Choose a mobile device such as iPhone or Galaxy
4. Refresh the page and see the innerWidth/innerHeight values

What is the expected behavior?
The expected behavior can be seen when using the attached page  myScreenResponsive.html in step 1. instead. 
I expect to see innerWidth/innerHeight the same as the dimension values set for that device.

What went wrong?
I can see correct values for outerWidth/outerHeight, screen.width/screen.height, screen.availWidth/screen.availHeight but not for the innerWidth/innerHeight. 
When I use a responsive page I see correct values. 

The same problem appears when using the API with setDeviceMetricsOverride in an extension.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 65.0.3325.106 (Official Build) beta (64-bit) (cohort: Beta)  Channel: n/a
OS Version: 10.0
Flash Version: Shockwave Flash 26.0 r0

When testing a custom desktop page I can see that the innerWidth/innerHeight are correct but the outerWidth/outerHeight are wrong. 

Is this supposed to be like this? If yes, can you explain why? If not, can you fix please :)
 

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