With Firefox 41 (and higher), it's no longer possible to customize the page shown in a new tab via changing the preference browser.newtab.url in about.config. Because of the fact that hijackers abused the preference in the past, Mozilla decided to remove it (see bug 1118285). Fortunately, by removing it, Mozilla also introduced a new API to bring this functionality back to life as an add-on. This add-on allows the user to choose a certain page in a new tab.

New Tab Override (browser.newtab.url replacement) https://addons.mozilla.org/en-US/firefox/addon/new-tab-override/

This is also available using Classic Theme Restorer (Customize Australis) {web link} Restore squared tabs, appmenu, add-ons bar, small button view and more on Australis UI (Windows/MacOSX/Linux + Fx 29+).

Hi, open the Add-ons Manager (Ctrl+Shift+A) > Extensions/Plugins and look for and disable/remove anything 'Yahoo.' Also look in your PC's Control Panel > Programs for anything suspicious installed at the time this started.

For security reasons you need to use an add-on to make changes to the New Tab page, so some malware may have got installed. You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Hitman Pro
• ESET Online Scanner

Note that not all removal programs will detect all malware, so you may need to run several or all of them.

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

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

I'm sorry to have been so long in thanking you for your response.

Sorry to have taken so long to respond but thank you. Seems to be back to normal.

Glad to help. Safe Surfing.