hello, first of all only download firefox from its official location at getfirefox.com - there you can be sure that downloads will always be clean and don't come bundled with toolbars, adware or other crap...

in order to deal with sweetpacks, please go to firefox > addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc). also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there and run a full scan of your system with the security software that you have in place and different other tools like the free version of malwarebytes & adwcleaner.

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

If you downloaded Firefox from mozilla.org then it did not come with Firefox any version for any OS.

This was very likely bundled in with another software you downloaded and installed recently from say example download.com aka cnet as they have been bundling crap such as this with software lately.

Points of information.

• Firefox does not ordinarily contain such software. In fact where possible it tries to help protect users.
• sweetpacks now blocklisted (bug 88147) by Firefox, although that does not help those already with such software.
• Users may also need to look in hidden folders, for such software
  • It may have some correlation with toparcade
  • related thread /questions/960863?page=2#answer-448693 it is a long thread but you may wish to scroll for information and links.
• To regain normal Firefox behaviour it may well be necessary to reset search engines after uninstalling the errant software
  • see Remove a toolbar that has taken over your Firefox search or home page and note the recommended addon searchreset

For links to uninstall information see

http://forums.mozillazine.org/viewtopic.php?f=38&t=2714237 

including http://malwaretips.com/blogs/remove-sweetpacks-toolbar/

• Registry edits:
  if anyone needs to resort to direct Registry hacks (some sites or threads may suggest this) please take great care and always ensure Registry backed up in advance of any edit.