The release notes for version 8.1.7729 state:
Added option to disable Viewer Controls when they aren't needed, so you can better see the Viewer contents.
How? I haven't been able to find the disable/enable.
In the Options dialog, Display tab. Show effect controls.
The checkbox mentioned above in the options dialog is for disabling it by default for all projects. If you only want to turn the viewer controls off temporarily you probably want to change Viewer panel > Options > Show Effect Controls.
Two good answers. Thanks!
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