Hi, it's possible that some malware has got in, so 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

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one. Windows 8 has antivirus built-in already.

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

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

After removal you may need to reset your New Tab, home page etc., which you can do by running the add-on SearchReset.

If your question is resolved by this or another answer, please take a minute to let us know. Thank you.

Thanks, but I'm afraid this didn't work. I have now also uninstalled Firefox. Searched for any files that had Firefox or Yahoo anywhere in the name and renamed them. Checked the startup folder to see if anything had been included there - it hadn't. Rebooted several times. Reinstalled Firefox (got it direct from mozilla.org so it wasn't a highjacked verison) - clicked on the new tab - and it was Yahoo that came up. Does anyone have any further suggestions? I don't want Yahoo, I am increasingly starting to hate Yahoo with a passion.

I ''THINK ''I might have found a resolution. I am including it here for other people's info. Went to the Control Panel in Windows Selected Uninstall a Program Clicked on the Installed On column to put everything in date order. Noticed that at the same time as I installed another piece of software a 2nd piece was installed without my permission. This was called Many Results Hub. Selected Many Results Hub and uninstalled. When doing this I noticed that it closed Firefox. After uninstalling, I rebooted the PC, just in case it left anything in memory Then once it rebooted again, I uninstalled Firefox (tbh, I probably didn't need to do this, but wasn't taking any chances) Rebooted again (probably didn't need to do this) Once the PC started itself again, I installed a clean version of Firefox.

Now, fingers crossed, that this has worked. If it has, I will come back in here tomorrow, and will mark this as solved.

That was very good work. Well Done. Please flag your last post as Solved Problem so others will know.

It’s very sad, but many of the software down-loaders / installers will trick you into installing not only their program, but other programs as well. You have heard of the fine print in shady contracts, right? Well, some installers you need to look at the itsy bitsy teeny weeny fine print. You are thinking you are giving the installer permission to install the program you want by using the recommended option. But if you use the Manual Option Instead, you discover all kinds of stuff that you do not even know what it is or what it does. From now on, everyone needs to Use The Manual Option to put a stop to this.