John's Infrequent Blog

{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 quotation marks)
Highlight the ICQ string > right click and choose reset
This ought to reset to Google, Bing, etc.

Then go to the Firefox view menu > Toolbars
Should ICQ still appear, make sure it is unchecked

Restart Firefox and the search box toolbar on the lower left of the toolbar section ought to be gone, your Search provider ought not to be ICQ.
Click on the down arrow of your search bar > manage search engines
Should ICQ persist in sitting there, highlight it and choose remove

NB Should this work but, upon opening a new blank tab you find the damned ICQ dialogue, go here in Firefox:

Tools > add ons > extensions > look for a Java Console for the ICQ toolbar > disable

Restart Firefox

It's a pesky thing but can be defeated.