As the reporter of the duplicate bug 1799787, I thought that I would see if I could reproduce this problem with the latest disco daily (20181205). Unfortunately I can by taking the following steps:
1. Boot to live session
2. Make external monitor the primary display and the laptop's internal monitor the secondary display
3. Install GNOME Tweaks
4. Enable 4 static workspaces
5. Enable workspaces span displays
6. Move to workspace 4
7. Open Firefox
8. Restart GNOME Shell with Alt F2 and enter
Both displays went blank and I was returned to the log in screen just as per my original report.
As the reporter of the duplicate bug 1799787, I thought that I would see if I could reproduce this problem with the latest disco daily (20181205). Unfortunately I can by taking the following steps:
1. Boot to live session
2. Make external monitor the primary display and the laptop's internal monitor the secondary display
3. Install GNOME Tweaks
4. Enable 4 static workspaces
5. Enable workspaces span displays
6. Move to workspace 4
7. Open Firefox
8. Restart GNOME Shell with Alt F2 and enter
Both displays went blank and I was returned to the log in screen just as per my original report.