UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:58.0) Gecko/20100101 Firefox/58.0

Steps to reproduce the problem:
1. Inspect a website in dev tools
2. Turn on device mode by clicking the icon next to the select tool
3. Toggle device mode off, then back on again.

What is the expected behavior?
The website should be shown in the mobile/responsive view each time that device mode is turned on. A refresh may be required to ensure that the styles are shown properly.

What went wrong?
On the second and all subsequent times that device mode is turned on, only half of the page is shown in the 'viewport'. The top-right, bottom-left and bottom-right quarters of the 'viewport' are blank. This is not fixed or helped by refreshing the page; the only solution is to close the tab and reopen the website in a new tab.

Did this work before? Yes 

Chrome version: 65.0.3325.146 (Official Build) (64-bit)  Channel: n/a
OS Version: OS X 10.13
Flash Version:
 

Deleted: Screen Shot 2018-03-14 at 17.30.13.png 260 KB

	Screen Shot 2018-03-14 at 17.30.13.png 260 KB View Download