One potential cause of unexpected pop-ups is an extension. Try disabling ALL nonessential or unrecognized extensions here:

orange Firefox button (or Tools menu) > Add-ons > Extensions category (in the left column, click Extensions)

Usually a link will appear above a disabled extension to restart Firefox. You can complete your work on the add-ons page and click the link as the last step.

I'm not sure what a homegroup is. Something new on Windows 8??

Firefox allows you to control both pop-ups and pop-unders through the Content panel in the Options window. Pop-up blocking is turned on by default, so you don't have to worry about enabling it to prevent pop-ups from appearing in Firefox.

When blocking a pop-up, Firefox displays an information bar (if it hasn’t been previously dismissed — see below), as well as an icon pop-up-icon-win in the location bar. popup-win7 When you click either the Options button in the info bar or the icon in the location bar, a menu is displayed with the following choices:

   Allow/Block pop-ups for this site
   Edit Pop-up Blocker Options…
   Don't show info bar when pop-ups are blocked
   (show the blocked pop-up) 

Blocking pop-ups may interfere with some websites: Some websites, including some banking sites, use pop-ups for important features. Blocking all pop-ups disables such features. To allow specific websites to use pop-ups, while blocking all others, you can add specific websites to the list of allowed sites. Blocking pop-ups doesn't always work: Although Firefox blocks most pop-ups, some websites may show pop-ups using uncovered methods, even when blocked. Pop-up blocker settings

To access the pop-up blocker settings:

   At the top of the Firefox window, click on the Firefox button and then select Options .
   Select the Content panel.

   Content Popup Win7 Fx23 

In the content panel:

   Block pop-up windows: Uncheck this to disable the pop-up blocker altogether.
   Exceptions: This is a list of sites that you want to allow to display pop-ups.

   86c0e1094489ddd5611008de57d0afed-1260046952-121-3.png
   The dialog has the following choices:
       Allow: Click this to add a website to the exceptions list.
       Remove Site: Click this to remove a website from the exceptions list.
       Remove All Sites: Click this to remove all of the websites in the exceptions list. 

Note: Blocking pop-ups may not always work and may interfere with some websites. For more information, see the What are Pop-ups? section above. Pop-ups not being blocked Is the pop-up coming from Firefox?

The pop-up may not actually be coming from Firefox. You can determine where the pop-up is coming from by the appearance of the window.

   If you see the location bar with the little bookmark star in the pop-up window, the pop-up is coming from Firefox. Another good indication is the Firefox logo or the orange Firefox button on Windows 7 in the top left corner of the window
   If not, you may have malware on your computer that causes the pop-ups. Scan your computer for viruses and spyware. For more details, see Troubleshoot Firefox issues caused by malware. 

Popup Win3 Is the pop-up blocker on and enabled for this site?

   At the top of the Firefox window, click on the Firefox button and then select Options
   Select the Content panel.
   Make sure the Block pop-up windows checkbox is checked.
   To the right of Block pop-up windows, click the Exceptions... button. A dialog will appear that shows all the sites that are allowed to show pop-ups.
   If the site that's opening pop-ups is in the list, select it and press Remove Site.
   Click Close.
   Click OK to close the Options window . 

Is the pop-up shown after a mouse click or a key press?

Certain events, such as clicking or pressing a key, can spawn pop-ups regardless of if the pop-up blocker is on. This is so that Firefox doesn't block pop-ups that websites need to work. Is it a true pop-up window?

Sometimes ads are designed to look like windows, but really aren't. Firefox's pop-up blocker can't stop these ads. fake-popup-win7

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Hi,

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Hi to block pop ups completely here's how:

Disabling all popups in Firefox

  Type "about:config" (without the apostrophes) in the browser's address bar and hit the enter key.
  First time users need to confirm that they be careful on the next page.
  Type or paste "dom.popup_allowed_events" (without the apostrophes) into the search field.
  The value of the preference highlights all events that are allowed to spawn popups.
  Double-click the preference and "REMOVE" some or "ALL" of the items here. You can also add some if you want to do so.

note if you are successful, the next time a pop up comes you can set to disable notification from appearing.

Go to the Mozilla Add-ons Web Page (There’s a lot of good stuff here) and look for a good add / pop-up blocker.