''As a Firefox user:'' You can "tear off" a tab in two ways: * click on the tab and drag downwards, and Firefox should move it to a new window * right-click the tab and choose Move to New Window However, if you are tearing the tab off from a maximized window, the new window also will be maximized rather than a resizable window that would be more like a pop-up. ''As a website:'' You can bypass the normal setting of diverting a new window to a new tab by specifying features of the window, for example, by setting a size. This demo page has examples: https://jeffersonscher.com/res/popit.html Firefox does have a hidden preference users can change in about:config (browser.link.open_newwindow.restriction) to override the "features" exception and force even those windows into a new tab. This could be why more sites are using in-page overlays rather than pop-ups, to ensure that dialogs appear in a useful manner.