Does Firefox not support the oncontextmenu event on SVG (JS without frameworks)?

Question

The propose is to call a contextmenu made by me (myCtxMenu) "attached" to a <text> SVG element, using Javascript (no frameworks). Something like this:

document.oncontextmenu = function() { // disable of default contextmenu
    return false;
}

(...)

var groupSignal = document.createElementNS("http://www.w3.org/2000/svg", "g");

var gsignalID = "gsignal1";
groupSignal.setAttribute("id", gsignalID);

svg.appendChild(groupSignal);

var txtNameSignal = document.createElementNS("http://www.w3.org/2000/svg", "text");

(...)

txtNameSignal.setAttribute('oncontextmenu', 'return myCtxMenu(' + gsignalID + ')');
groupSignal.appendChild(txtNameSignal);

The problem is that this code runs perfectly on Chrome but not on Firefox. :(

If I change the attribute to "onclick" or "onmouseover", instead of "oncontextmenu", it works perfectly on both browsers, e.g. it calls myCtxMenu (my custom contextmenu).

Any idea to workaround this issue?

Thanks!