Make use of Addons..
pop up blocker and Ads block.
https://addons.mozilla.org/en-US/firefox/addon/adblock-plus-pop-up-addon/

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.

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

I have installed Ad Blocker plus as an add on. I have reset Firefox to the default settings. I still have Chitka ads popping up in the lower right corner blocking site content on certain sites and with no "x" to delete it.

Here is the coding that comes with the ad:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><style type="text/css">.clear{display:block;clear:both;height:0;line-height:0}.popupFooter{background-color:white;position:fixed;z-index:1000;bottom:0;margin-left:15px;width:690px;border-left:1px solid #a7a9ab;border-right:1px solid #a7a9ab;border-top:2px solid #036;padding:14px 16px;box-shadow:0 0 12px #000;-moz-box-shadow:0 0 12px #000;-webkit-box-shadow:0 0 12px #000}.popupFooter *{font-family:Arial,Tahoma,Verdana,sans-serif;margin:0;padding:0;border:0;outline:0;vertical-align:baseline}.popupFooter a{text-decoration:none}.popupFooter a:hover{text-decoration:underline}.popupFooter div{font-size:12px;line-height:16px}.popupFooter .navTop{position:absolute;top:9px;right:10px;width:80px;}.popupFooter .navTop a{display:inline-block;vertical-align:middle;margin-left:2px}.popupFooter .navTop .btnClose{width:14px;height:14px;background:url(http://www.google-analytics.com/img/newch/iconsPopup.png) no-repeat -14px 0 transparent}.popupFooter .navTop .btnHelp{width:14px;height:14px;background:url(http://www.google-analytics.com/img/newch/iconsPopup.png) no-repeat 0 0 transparent}.popupFooter .section{padding:0 10px 16px 15px}.popupFooter .section .btnClick{margin-top:-8px;float:right;display:block;background-color:#053769;color:#fff;height:22px;border-top:1px solid #579;border-bottom:1px solid #012b56;line-height:22px;padding:0 15px;font-weight:bold;border-radius:3px;-moz-border-radius:3px;-webkit-border-radius:3px}.popupFooter .section .btnClick:hover{background-color:#00478e;text-decoration:none}.popupFooter .section .name{font-size:14px;padding-bottom:6px}.popupFooter .section .name a{color:#12c}.popupFooter .section .webAddress a{color:#093}.popupFooter .section p{color:#222;padding-bottom:2px}.popupFooter .ttl{color:#4e4e4e;font-size:18px;line-height:20px;padding-bottom:20px}</style><div id="popupFooter" class="popupFooter"><div class="navTop"><a href="#">Chitka</a><a href="#" id="btnHelp" class="btnHelp"><!-- --></a><a href="#" id="btnClose" class="btnClose"><!-- --></a><div class="clear"><!-- --></div></div><div class="ttl">Searching for hot air mar pm update obama?</div><div class="section"><div class="name"><a href="#">hot air mar pm update obama</a></div><p>Learn How to Eat Smart & Exercise to Lose Weight and Prevent Diseases. Get Info!</p><div class="webAddress"></div><a href="#" class="btnClick">Click here</a><div class="clear"><!-- --></div></div></div>

When you right click on this ad, neither Ad Block plus nor Super Ad Blocker, which I also have installed, offers the opportunity to block this ad.

I also have Avira antivirus and MalawareBytes installed on my Windows 7 machine. They detect nothing.

Everything has the latest updates, including Firefox.

Any ideas?

Do a malware check with some malware scanning programs on the Windows computer.
Please scan with all programs because each program detects different malware.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender: Home Page:
  http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• http://support.kaspersky.com/viruses/solutions?qid=208280684

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

Try a clean reinstall and delete the Firefox program folder before reinstalling a fresh copy of Firefox.

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 19.0.x: http://www.mozilla.org/en-US/firefox/all.html

Uninstall your current Firefox version, if possible, to cleanup the Windows registry and settings in security software.

• Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other profile data are stored in the Firefox Profile Folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.

If you keep having problems then also create a new profile.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall