Bad link in civicrm/case/activity/view breadcrumb
Disable popups in display preferences.
Find a case eg civicrm/case/search?reset=1.
'Manage' the case to open it.
Click on the activity Subject, goes to eg civicrm/case/activity/view?cid=203&aid=642
The 'Case Activity' breadcrumb links to civicrm/case/activity?reset=1 which gives an error when you try to use it:
Sorry, due to an error, we are unable to fulfill your request at the moment. You may want to contact your administrator or service provider with more details about what action you were performing when this occurred. required params missing.
Can reproduce this on http://dmaster.demo.civicrm.org
To upload designs, you'll need to enable LFS and have admin enable hashed storage. More information