Cannot edit any of the external gadget on dashboard. Editing form element doesn't show up when selecting "Edit" from external gadget's Gadget Menu.

This issue may be different from JRA-34274 as it doesn't have any JS exceptions.

A little bit debugging and it turned out that form has unwanted "hidden" class defined. Show/hide toggle is managed with css display: block/none. But "hidden" class is more important and form stays hidden.

At the moment the template that I can see from browser resources is:

<form action="${userPrefs.action}" class="aui userpref-form hidden" method="post" id="gadget-${id}-edit">

But should be without hidden class:

<form action="${userPrefs.action}" class="aui userpref-form" method="post" id="gadget-${id}-edit">

For example on dashboard:
-> "+ Add gadget"
-> find "JIRA: News"
-> "Add it now"
-> "Close" dialog
-> Open "Gadget Menu" dropdown from gadget upper right corner
-> "Edit"