There are two parts to this solution. Pay attention. One is easy and well know but it's ineffective for the popunders. That's taken care of in part two. The popups come from the browser AND the plug-ins. You need to take care of the plug-in problem. See both parts for the complete solution.

Part 1.

If you're running Mozilla Firefox and with to adjust or change how Firefox handles pop-up follow the below steps.

  1. Open Mozilla Firefox
  2. Click Tools
  3. Click Options
  4. Click the Web features button on the left hand side of the Options window.
  5. By default this feature should be enabled if you wish to disable the feature, uncheck "Block Popup Windows." If you have allowed popups on a site you wish to now block you can also click "Allowed sites" in this window and remove any sites you wish to block any popup on.

Part 2.

Users may also wish to disable any popups from from any browser plug-ins, a tactic for bypassing many popup blockers. To enable this feature in firefox follow the below steps.

  1. Open Mozilla Firefox
  2. In the URL field type "about:config" and press enter.  Instead of www.blah.com (Same Location)
  3. This should open the Firefox config window.
  4. Right-click in the main portion of the window and click "New" and then "Integer"
  5. For the preference name type "privacy.popups.disable_from_plugins" and click Ok.
  6. For the value type "2"

Finally, I suggest you locate the "privacy.popups.firstTime" option also in the about:config screen and change the value of this setting to "false"

Then close the broswer and restart.

For Netflix pop-under advertisements specifically, you need to CLICK TO OPT OUT on the right side of this page.
http://www.optmd.com/

The opt out is not necessary if you execute part two. In fact, the optmd.com relies on tracking cookies being on. This is a red herring created by the people who make the pop-under ads to continue to track you. Even though you "opt out" they still get your information and generally more because your cookies have to be on or open in order for their pop under stopper to work. In general, the pop under executes specific code that is browser dependent. The netflix version exploits this and executes the same code. They all have to execute the same commands in order to get the pop-under window to show up. I recommend for security reasons you do not use the www.optmd.com solution.