In Tools > Options > Content > check "Block Popup Windows" .

If the above is not helpful try the awesome Adblock Plus add-on

see also for info: Popups not blocked

thank you

Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.

It is more like an ap that has hijacked my browser. i.e. on the Southwest airlines website, I do not get this if I use Explorer or Firefox on another PC (see attached image).

First, try to reset Firefox. Refresh Firefox - reset add-ons and settings. This simple step will eliminate many Firefox problems with only one click.

A few other basic trouble shooting things you can try is this: Run all Windows Updates, install all needed service packs, etc.

Update your graphics driver (Firefox uses your graphics card for some rendering, and an out of date graphics card driver can cause problems. Upgrade your graphics drivers to use hardware acceleration and WebGL

Update all your plugins (Flash, Java, etc.): http://www.mozilla.org/plugincheck/.

Download and Install MalwareBytes Anti-Malware, run a full Scan. http://www.malwarebytes.org/. This helps check that there are no viruses on your computer causing issues. You can uninstall this program after you clean off any infections.

Download and Run TDSSKiller http://support.kaspersky.com/faq/?qid=208283363

Download and Install Microsoft Security Essentials http://windows.microsoft.com/en-US/windows/products/security-essentials (not an official endorsement, but I personally recommend MSE as an awesome permanent anti-virus)

I got rid of it by going to Tools -> Add-ons and then the Extensions tab and removed YonToo.

This also got rid of Drop Down Deals too.