It sounds like you have a third party program that has taken over your search engine, home page, and/or the default new tab page. Fortunately, this can be remedied easily:

1. At the top of the Firefox window, click on the Firefox button (Tools menu in Windows XP), and then click Add-ons. The Add-ons Manager tab will open.
2. In the Add-ons Manager tab, select the Extensions panel.
3. Select the toolbar you wish to remove.
4. Click the remove button.
5. Click "Restart now" if it pops up. Your tabs will be saved and restored after the restart.

After Firefox restarts, install the Search Reset Tool. This will remove the rest of the traces of this program from your Firefox.

For further information, please read Remove a toolbar that has taken over your Firefox search or home page.

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Hello,

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information.
Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

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Thank you.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Also try ADW Cleaner

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

dosearches had appeared when i fired up FireFox (Right Mouse click the Firefox Icon select properties and you will likely see dosearches added to the target (remove it), that was easy to fix. However it was also appearing each time I clicked new tab. This drove me crazy because I could see no add-on or option to configure but here is the fix.

type about:config as url then type in newtab into the search box you will see browser.newtab.url appear edit this to remove dosearches.com then put in the URL you prefer. Thanks dosearches because I've always wanted to know how to configure the new tab button

It may also append the rogue site URL to the shortcut Firefox uses see also /questions/979036#answer-506688