There's a good chance this is caused by an extension. Try this:

Disable ALL nonessential or unrecognized extensions on the Add-ons page. Either:

• Ctrl+Shift+a
• orange Firefox button (or Tools menu) > Add-ons

In the left column, click Extensions. Then, if in doubt, disable.

Usually a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Does that get rid of the ads?

Unknown or suspicious extensions often get installed as part of a bundle with some freeware. It would be a good idea to:

(1) Check the Windows Control Panel, Uninstall a Program, and click the "Installed on" column heading to see what has been installed recently.

(2) Mop up with some supplemental malware scanning tools. This article lists programs that other Firefox users have found useful: Troubleshoot Firefox issues caused by malware.

The forum software detected your Firefox as version 22. Is that correct?

Version 22 is not secure; Mozilla discloses security flaws after each new release. Is something holding you back from upgrading to Firefox 27? Please let us know so we can suggest solutions or workarounds.

If Help > About Firefox shows Firefox 27.0.1, you may need to clear a hidden setting that is causing Firefox to misreport your version number. See: How to reset the default user agent on Firefox.

When I search for pages that mention that website popping up, I find one related to a rootkit, which can be very difficult to remove. Hopefully the explanation is more innocent in your case. More information:

• http://forum.webuser.co.uk/showthread.php?t=128842
• http://malwaretips.com/blogs/remove-zeroaccess-rootkit/
  WARNING: Using COMBOFIX without assistance can cause broken Windows

Please note that removal of rootkits and other deeply embedded malware is beyond the scope of this forum. There are some suggested forums in the troubleshooting malware article I linked above.