Web developers can use the optional
windowFeatures parameter for the
window.open method to define how a new tab or window should be displayed to the users, though the behaviour is implementation-dependent.
Starting with Firefox 76, it will no longer be possible to control the browser’s user interface elements with certain window features such as
toolbar, which were only supported by Firefox and Internet Explorer. This change aims not only to align with other modern browsers but also to avoid unexpected behaviours due to UI customization or session restore.
These window features continue to be used as conditions for Firefox to decide whether to open a new tab or popup window.