Dialog - Form dialog on firefox

[antuxity]

On Firefox, when a form dialog is longer than the height of the dialog. When I scroll down and click on different window then click back on the original browser with form dialog. It causes the content scroll up to the first input field of the form. This seem to happen on Firefox

Can be tested on the demo page (​http://jqueryui.com/dialog/#modal-form) -Click on [Create new user] -Resize the dialog so it can have vertical scroll bar. -Scroll down to the bottom -Click outside the browser (cause the browser window to be inactive) -Click on same blank or text area on to the dialog (it will cause the content scroll back on top with first input box focused)

[tj.vantoll]

Duplicate of #9101.