Newsletter extension helps users to - create newsletters, create issues for those newsletters, make other users publishers of the newsletters and many other related activities. One of the special pages which delivers these functionalities is Special:ManageNewsletter wherein you can remove a publisher of a newsletter. On clicking the 'Remove' button you remove a publisher of the newsletter if you have the right for it. This task requires you to add a confirmation box when the remove button is clicked asking the user who is removing the publisher whether he/she is certain of the removal (just like the dialogue boxes you get when you close the browser when mulitple tabs are open).
# Install Mediawiki (https://www.mediawiki.org/wiki/Manual:Installation_guide#Main_installation_guide)
# Install Newsletter extension (https://www.mediawiki.org/wiki/Extension:Newsletter)
# Navigate to Special:ManageNewsletter, add few publishers(can be dummy users you created)
# Click the remove button in the table and see how a publisher is removed right away without giving a second chance to the user to rethink the decision.