There are a few ways you might have lost your mini buttons.

First, in the global settings (under Interactions) there is a switch to disable the mini buttons entirely. 

Make sure this is turned on:

If this is on and you still don't see them, check if you have enabled your device to recognize touch events (also under Interactions). If so, Marvin thinks you are on a touch device and hides the mini buttons by default:

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