I think you are saying that your 'home page'; has been hijacked by sweet1m - there is also a search engine hijack it can do but you have not described that since you say the search box is still 'Google'. It appears to be associated with 'smilies' on instant messaging like MSN and yahoo and is thought to be harmless (but annoying!). I understand from your reply that 'blecko' is also coming up as a browser page and not just a search box item?
You have done this?
1) Use Add/Remove Programs from Control Panel in Windows to remove sweet1m and blecko (if they are there)
2) In Firefox go to Tools/Add-Ons/Extensions and uninstall the SweetIM and blecko extensions (if they are there)
3) Go to your search engines and find Manage Search Engines then delete the SweetIm search engine from the list. (JUST IN CASE!)
4) In Firefox go to Tools/Options and look at the Main tab. Be sure that your home page URL has not been hijacked.
If that does not fix it, run malwarebytes in Windows Safe mode and see.
Can you report back then?