That may be pop-ups that are opened with specific dimensions via JavaScript window.open() calls.

See:

• http://kb.mozillazine.org/browser.link.open_newwindow.restriction

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.

• Use the Filter bar at to top of the about:config page to locate a preference more easily.
• Preferences that have been modified show as bold(user set).
• Preferences can be reset to the default or changed via the right-click context menu.

Thanks. But why should this need to be manually fixed in about:config? It seems like an oversight or a bug; I can't see how any user would enjoy this new behavior, and it is a new behavior.