If you are getting pop-ups and pop-unders, which are mostly Flash based, you can try this tweak.

To block pop-ups from plugins, open your Firefox browser.

1) Type about:config in the address field.
2) Right-click in the resulting config page somewhere and select New -> Interger. 3) Type privacy.popups.disable_from_plugins in the resulting dialog, hit OK,
4) Type 2 in the next dialog and you're all set.

This pref can actually take three values:

• 0: open allowed
• 1: the opened windows are treated as popups, but they're allowed to open (we limit the number of these types of popups)
• 2: the window is a popup, block it