Hi all,
In 4.8 and beyond, you can set this behavior in Editor Preferences > Appearance. Look for Open Asset Editor Tabs in New Window option, and enable or disable it as you would prefer.
Additionally, there are two tab docking commands available in Editor Preferences > Keyboard Shortcuts for closing tabs: Close Major Tab and Close Minor Tab. By default, only Close Major Tab has a key set (Ctrl+F4), but you can set Close Minor Tab to a shortcut to easily close current window’s active minor tab.
Hope that helps!