When showing window it moves to the center of the screen from top left

Flow
1

When showing a modal window with a large number of components it appears in the top left corner then moves to the center of the screen. This behavior is typical for the Valo theme on Firefox browser. Tell who ever encountered this problem?

2

example video

3

I don’t know how you have aligned your model window. I tried to reproduce your situation
and could not reproduce it in Firefox v45.0.2

Perhaps if you try something like this:

        Window win = new Window();
        win.setWidth("600px");
        win.center();

Would it still display such behavior?

4

This problem is noticed on unbuntu 16.04 and firefox 45.0.2 and Vaadin 7.6.4

Window win = new Window(); win.setWidth("600px"); win.center(); Sample code given by you has not solved the problem.
The form must be with a large number of components and size 1300X800 for example.