Citrix doesn’t play well with Safari on a Mac. Apparently Citrix still thinks that Macs should be running IE5 (there’s a blast from the past), because in order to use Safari with Citrix, you have to “pretend” to be using IE.
To do this, you have to enable the “Develop” menu in Safari, which is hidden by default.
Run Terminal and type (or copy/paste):
defaults write com.apple.Safari IncludeDebugMenu 1
Hit enter. Now open Safari. The Develop menu should be there now. Select one of the IE browsers under User Agent, and now Citrix should be satisifed that you are actually running a Mac.
In actual practice, Firefox is still a better option for Citrix Mac users, since with Safari you will have to select the User Agent everytime you want to use Citrix. Safari goes back to its default user agent settings when you close it.