Complete the following change within Firefox to resolve the issue:
  1. Open the Firefox browser
  2. Enter about:config into the Firefox address bar and press enter
  3. Click "I'll be careful, I promise!"
  4. In the search field enter plugins.load_appdir_plugins
  5. Double click the line to change the "Value" column to read "True"
  6. Close all instances of Firefox to restart the browser
  7. Users will no longer receive the prompt to install Citrix and will be able to successfully launch hosted applications

If the issue persists, Click Chat with Support and reference this article.