'To' field not populated in the 'email contact' screen upon clicking on email in contact screen
Figured it out: In Administer >> Customize Data and Screens >> Display Preferences: The WYSIWYG field was set to "Joomla Default Editor" (it didn't matter what the default editor in Joomla's Global Configuration was set to - tried them all and the issue kept occurring).

When I set WYSIWYG in CiviCRM's Display Preferences to "CKEditor" or "TinyMCE" all is well.