Modals Stop Working When Upgrading to 2.5.0
From Joomla! Documentation
When upgrading from 1.7.3 to 2.5.0, modal "pop-ups" may stop working and be displayed full-page (as seen below) with the Save, Save and Close, and Cancel buttons unresponsive.
This issue is caused by changes to the Administrative template. The fix is to clear your browser's cache. For specific instructions on how to do this, please see: