dragstart event gives error: Permission denied to access property "effectAllowed"

I just started to work with meteor (1.1.0.2) and try to implement some drag and drop functionality. Basically what it should do: The user can drag video element from a sidebar to a contenteditable div.

My problem is now that it is not working in firefox (v 37, OSX) but it is working in Chrome.

Here is some Code:

Template.single_video.events(
{
  'dragstart video': function(event)
  {
        var dt =  event.originalEvent.dataTransfer;
    dt.effectAllowed = "copy";
        dt.setData('text/html', e.currentTarget.outerHTML);

        return false;
  }
})

<template name="single_video">
        <div class="col-xs-12">
                {{title}} 
                <video controls="" class="video-drag" draggable="true">
                        {{#each sources}}
                                <source src="{{src}}" type="{{type}}">
                        {{/each}}
                </video>
        </div>
</template>

I always get the error: Error: Permission denied to access property "effectAllowed"

So my question is: Is it a bug in FF or did I miss something? Thanks in advance for any help.