In Firefox use the following steps.
  1. Click on the open menu icon (three bars found on the top right). 
  2. Click on the options icon (looks like a gear). 
  3. Click on the Applications tab.
  4. Look for "Citrix ICA Client" under the Content Type column.  Click on it. 
  5. This will highlight/select it for modification. Click on the drop down arrow under the Action column and next to the words "Use Citrix ICA Client (default).
  6. Change this to "Use Citrix Connection Manager" by clicking on it. Click the ok button to make the changes. 

You should be able to now launch FIMS. On some systems you may need to log out of Hostnet and close the browser.  Then try again.