This.getDoc () is null in FF using tinymce

I had a problem: when I load my page, I immediately get an error: this.getDoc() is null

The getBody()of function Editor.jsis called and the document seems inaccessible

getBody : function() {
    return this.bodyElement || this.getDoc().body;
},

In this case, the getBody () function is invoked by the destroy () function in the gecko code block.

destroy : function(s) {
        var t = this;

        // One time is enough
        if (t.destroyed)
            return;

        // We must unbind on Gecko since it would otherwise produce the pesky "attempt to run compile-and-go script on a cleared scope" message
        if (isGecko) {
            Event.unbind(t.getDoc());
            Event.unbind(t.getWin());
            Event.unbind(t.getBody()); // here is the relevant getBody() call
        }

Destruction caused by addUnload tinymce.js function

o.func.call(o.scope, 1);

What can I do to avoid this problem?