can not delete http://websearch.youwillfind.info/?r=2013/04/28 when open new tab...
please help delete it...
Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.
You can try these free programs to scan for malware, which work with your existing antivirus software:
Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.
Further information can be found in the Troubleshoot Firefox issues caused by malware article.
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Try to use the SearchReset extension to reset some preferences to the default values.
Note that the SearchReset extension only runs once and then uninstalls automatically, so it won't show on the "Firefox > Add-ons" page (about:addons).
If you do not keep changes after a restart then see: