Mozilla's Pop-up Blocker is integrated into the browser, much like the Pop-up Blocker for Internet Explorer. To disable the Pop-up Blocker:
Open the Tools menu and click on Options.
The following window will appear:
Click on the Web Features icon in the list on the left.
Remove the checkmark from beside the Block Popup Windows option.
Click OK to close the window.
Once you are finished, you can go back into the menu again to turn on the Pop-up Blocker.