Pop-Up Blocker is only available for Yahoo! Toolbar version 5.6 and newer for Internet Explorer. Mozilla Firefox has its own pop-up blocker built into the browser.

To make sure it's enabled:

1. Select "Options" from the "Tools" menu.
2. Select "Web Features" in the left pane.
3. Check "Block Pop-Up Windows" if there is no checkmark next to it.

If you're still receiving pop-ups, click on "Allowed Sites" and remove any sites you don't use regularly.

If you still receive pop-ups, either pop-up authors have discovered a new way to display them that isn't blocked, or you have adware installed on your computer. Try running Yahoo! Anti-Spy, or another spyware scanner, to find and remove any adware on your system. Also, check getfirefox.com to make sure you have the most recent version of Firefox installed and for assistance in using Mozilla Firefox.