Have you tried clearing your browser cache in IE? After disabling SSL in Tableau Server, you should be able to access via http - like you can in Firefox. I'm not sure what in the IE settings could be forcing you to https, but if clearing the cache doesn't work, maybe someone on your IT team familiar with your IE settings would have an idea?
Thanks, Carisa! That's exactly what it was. IE is typically not my default browser, so I forgot about this setting.