You can move tabs to another window or a new window from the right click menu on tabs.
Not only moving the clicked tab, you can move
Tabs on the right side of the clicked tab
Clicked tab and the right side tabs
Tabs on the left side of the clicked tab
Clicked tab and the left side tabs
All tabs
Tabs selected in a popup window
By moving all tabs in one window to another window, you can merge two windows. Pinned tabs remain pinned after moving. Optional notifications show progress.
For addons developers: You can use this addon through sendMessage. For details, see README.
