Do not set focus on date when input changed for Firefox

Firefox fires a change event when user use the navigation per month and year.
So we can not set the focus on the date entry without closing the input picker.
In order to navigate with tab after picker is closed, we must ensure to not
have the focus on the icon.

issue11715
review426031003

src/view/form.js

@@ -1691,7 +1691,10 @@ function eval_pyson(value){
                     value = this._parse(this._input_format, value);
                     value = this._format(this.get_format(), value);
                     this.date.val(value).change();
-                    this.date.focus();
+                    if (!~navigator.userAgent.indexOf("Firefox")) {
+                        // Firefox triggers change when navigate by month/year
+                        this.date.focus();
+                    }
                 }
                 this.send_modified();
             });
@@ -1700,6 +1703,7 @@ function eval_pyson(value){
                     'class': 'icon-input icon-secondary',
                     'aria-label': Sao.i18n.gettext("Open the calendar"),
                     'title': Sao.i18n.gettext("Open the calendar"),
+                    'tabindex': -1,
                 }).appendTo(group);
                 this.input.appendTo(this.icon);
                 Sao.common.ICONFACTORY.get_icon_img('tryton-date')