How do you remove the Firefox limit on (20) popups?

1. Open a new tab and type into the address bar about:config?filter=dom.popup_maximum and press Enter. If you receive a warning, click the button that says “I’ll be careful, I promise”.
2. Double click on the dom.popup_maximum preference and a popup will appear.
3. Change the value to your choice (default is 20) and press OK.

More information on the preference.

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http://superuser.com/questions/477183/how-do-you-remove-the-firefox-limit-on-20-popups