Currently, there is no way to either: hold click a tab and create a new window and drag another window tab and join it with another window. Much like many browsers like chrome. This would be an amazing feature as it would allow someone to open many separate files all into aseprite without going into aseprite, and clicking open, and then using the built in file explorer.
Many thanks for the developers incredible feedback to the community yet again,
Dan.
There are plans for a Chrome-like interface, but is something really hard to implement at the moment. There are some issues related to this: