This page was designed to test the basic popup blocking features in Mozilla & Mozilla Firefox, it will attempt to create one popup initially and another after a three second delay. If you are using a current release of Mozilla (or a browser with a popup blocker), you shouldn't see anything at all.

In addition to the above, a secondary test exists which can run the same two popups, but only when requested (the result of a click event). Most of the time, you'd want to see user-requested popups as they may display documentation, screenshots, or other useful information. A sane popup blocker should display the first popup, but not the second.

Mozilla Firefox (0.8+): click Tools -> Options -> Web Features and check Block Popup Windows.

Mozilla (1.6+): click Edit -> Preferences -> Privacy & Security -> Popup Windows and check Block unrequested popup windows.

Current releases allow the customization of events that can trigger popups:
  dom.popup_allowed_events -> 'click submit'

Some sites are using plugins to initiate popups, which are not blocked by default (in Firefox 1.0). Setting privacy.popups.disable_from_plugins to 2 will do the trick, but this will block all plugin-related popups, requested or not.

   Note: The dom.disable_open_click_delay pref (below) may also prove useful.

Older releases may need the following to be set in about:config or <profile_folder>/prefs.js:
  dom.disable_open_click_delay -> 1000
  dom.disable_open_during_load -> true

Tests: automatic (page reload) or click (requested)

On a semi-related note, links with target="_blank" or target="_new" can be forced to load in the same window with the following: -> 1

Older releases (Mozilla <= 1.7, Firefox <= 0.9):
  browser.block.target_new_window -> true

Tests: target=_blank or target=_new

Related: Test your pop-up killer,, Webroot's Pop Up Tester, Pop-Up Stopper, AdBlock.