Asa Dotzler wrote in to tell us that the Mozilla Foundation is testing a patch for Mozilla Firefox that improves popup blocking. In a recent weeks, a number of advertising networks (once again, we won't mention Fastclick by name) have started exploiting the fact that Firefox's popup blocker doesn't stop popups launched by plugins (for example, Flash movies) by default. The patch, which is available as a signed extension for testing purposes, adds no new functionality but does change a couple of hidden preferences. The value of privacy.popups.disable_from_plugins is changed to 2, meaning that plugins are not allowed to open new windows, and the value of dom.popup_allowed_events is changed to an empty string, which stops all Web page events (such as clicks and form submissions) from launching popups. This means that some user-initiated popups (the type you generally want) may now be blocked. There are also reports that the extension breaks the ability to open blocked popups from the yellow bar or popup blocker Status Bar icon. You can still whitelist sites that you wish to allow to use popups.
To test the popup blocker changes, install the Popups Must Die! extension. Read Asa's weblog posting about the extension for more information. Feedback should also be sent to Asa.
This isn't the first time that the popup blocker has been modified in response to the evil tricks of webmasters. When the feature first debuted, it simply blocked all popups triggered by page loads, page unloads and timeouts. Since then, it has been enhanced to block popups triggered by a wide variety of events and also limit the number of simultaneous popups allowed.
