{The easiest method is to do a system restore to a time before the installation but as you're here you probably cannot do that}
 
Should you wish to delete ICQ, first go to add/remove programs (where you'll need to delete both the toolbar and the application)
Restart Firefox and, should ICQ still remain:

Open a fresh Firefox tab, In the URL address bar type "about:config" (not the quote marks) > notice the warning message > do be careful
In the "Filter" box type : "keyword.URL" (without quotatio...