Steps to reproduce: Use Chrome (not Firefox). Go to a page that contains maps with static map thumbnails, e.g. https://en.wikipedia.beta.wmflabs.org/wiki/Maptests. Use the tab key to navigate to one of the maps. Try to press enter on the fullscreen button in the top right corner. Nothing happens.
Pressing enter when the map is focused works. But not the button. Both should work.
It seems to work when the map is dynamic, e.g. on https://de.wikivoyage.org/wiki/Pirna.
Demo for fix:
https://en.wikipedia.beta.wmflabs.org/wiki/Maptests/Nearby
- Tab to fullscreen button and press enter.