Right-click in the editor does not work in Firefox on Widows

[ClementSparrow]

(works fine on mac or in other browsers)

Apparently the mousedown event is not triggered during a right click (but mouseup and click events are), probably because the event is replaced with a contextmenu event that P:S listens to and prevents (see src/js/addlisteners.js and function rightClickCanvas in src/js/inputoutput.js).