In my testcase the layer-group is still not displayed on the map, but at least it does not throw errors causing the map to not render anymore...

Added missing semicolon & <content></content> so children can actually be found.

leaflet-layer-group working

This property causes the map containing the Layer-Group to be automatically resized to fit the given container. Using more than one container with this set to true will probably cause random behaviour.

Needed for Firefox & Safari to work with dom-repeat.

Might be better to reregister the mutationObserver at the right point, but until now I did not see any issues.

Patch 1 - fix Safari & firefox issues