hello, you have adware present on your system please try these steps:

1. reset firefox (this will keep your bookmarks and passwords)
2. afterwards go to the firefox menu > addons > extensions and in case there are still extensions listed there, disable them.
3. finally run a full scan of your system with different security tools like the free version of malwarebytes and adwcleaner to make sure that adware isn't present in other places of your system as well.

Troubleshoot Firefox issues caused by malware

Also, Download the Mozilla Search Reset {web link} This add-on is very simple: on installation, it backs up and then resets your search preferences and home page to their default values, and then uninstalls itself. This affects the search bar, URL bar searches, and the home page.

Remove the Astromenda New Tab extension and reset your browser settings. Follow the removal guide here:

http://deletemalware.blogspot.com/2014/07/remove-astromenda-search-virus.html

Here's how to reset your web browser:

https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems

Finally, scan your computer with Malarebytes and AdwCleaner.

Cheers!

You may not have to reset the browser ! !

Use most or all of the listed programs below, and the search reset I posted before.

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 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.

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

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