On start of an application over NetMan HTML View the Citrix Web Client creates files with the extension ICA. The setup of the Citrix Web Client registers the mime type (MIME-Type application/x-ica) for the Internet Explorer, but not for other browsers. Clicking on an HTML View hyperlink may open a download box instead or show the content of the file as text.

Mozilla browser (Firefox / Netscape):

Mozilla browsers show a dialog box which offers the start with the "Citrix ICA Client". Additionally there is a check box which allows to do this for files with this extension next time automatically.
The mime type is registered in the browser settings.

Please also see the hints in the KB articles Operation mode of the RDP Web Client in dependence of different browsers and Mime type registering within HTTP server.