I've removed this pest from a colleagues laptop and the link in post #4 has the relevant tips that I used then:
Reset your Location Bar search engine (if typing a few words in the URL/Location Bar takes you to
SweetIM search):
- type about:config in your Location Bar, like typing a web site address, and press the Enter key
- ignore warning and choose to continue
- in Filter, type keyword.URL
- in lower part of screen, if it is bold and shows "user set", right-click keyword.URL and choose "Reset"
- in Filter, type SweetIM
- any items in lower part of screen in bold and showing "user set", right-click and choose "Reset"
- close about:config tab
I only had to search for 'SweetIM' and reset those values.