Do a malware check with some malware scanning programs on the Windows computer.
You need to 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.

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

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

This is how I removed DealCabby: Disabling DealCabby from Firefox: In the top menu, go to Tools > Add-ons > Select the DealCabby Toolbar logo > click Enable or Disable.

I found this info by going to: http://www.dealcabby.com/uninstall.php it is a safe page, with info on how to remove it. Many people have it on chrome, and with them was as simple as removing the extension.

I had the same problem, but I don't have DealCabby installed.

- In      Tools -> Options -> Content      I  unchecked the Firefox "Load Images Automatically".
- The text was still highlighted, but displayed the word "CouponDropDown".
- I correlated "Dropdown" with a program I installed called "DropBox".
- I uninstalled "DropBox".  
- The problem went away.
- In      Tools -> Options -> Content      I  re-checked the Firefox "Load Images Automatically".
- Problem is still gone.

Maybe DropBox can be installed without that feature. I don't know.

Zeus Of Coarsegold