As the latest upgrade of FireFox, not only homepage but also prompted page in new tab become seachnu.com. I am very unhappy about that. It is just like kidnapping, and interrupts my good user experience in FireFox.
After searching on google, to remove searchnu is not difficult. Just following the steps, it works.
1. Go to the Start Menu. Select Control Panel → Add/Remove Programs.
If you are using Windows Vista or Windows 7, select Control Panel → Uninstall a Program.
2. Search for Searchqu Toolbar in the list. Select the program and click Remove button.
If you are using Windows Vista/7, click Uninstall up near the top of that window.
3. Go to Tools → Options. Under the General tab reset the startup homepage or change it to google.com, etc.
4. In the URL address bar, type about:config and hit Enter.
In the filter at the top, type: keyword.URL
Double click keyword.URL. Delete search-results.com and replace it with http://www.google.com/search?ie=UTF-8&oe=utf-8&q=
(All information above refers to http://deletemalware.blogspot.tw/2012/04/remove-searchnu-uninstall-guide.html)