Context menu keyboard interactions in Firefox do not work

[ben-lu-uw]

i.e. right clicking on the map and pressing D does not toggle debug mode in Firefox but it does in Chrome.
Perhaps similar to issue #465.
event.keyCode is deprecated but is still supported by browsers.

[ben-lu-uw]

The usage of event.path is unsupported in Firefox. Using event.composedPath is the standard and fixes this issue and #465.