Wasn’t sure if this is best placed here or the Themes channel but we built an exhibit using the Freedom theme and discovered the following accessibility issues:
Header search box button lacks discernable text.
Showing # to # of # results text at bottom of items page fails color contrast.
The next release of Freedom will include a number of fixes to the Advanced Search form, including correcting that missing label on select[name="has_media"]. In-progress issues can be accessed in the theme’s repository if that might serve as a helpful resource to review against your own testing.
The iFrame issue is not theme-specific here and will be looked into for future updates to Omeka S. Thank you for catching that!