Firefox tabs: are they valid drag-n-drop entities?

Tried to d&d FF tab 开发者_运维知识库into notepad window. Above it, the cursor changed, showing that this can't be dropped here. Same behavior in Chrome.

Which Windows tools may be used to determine type of object prepared for D&D (if the window can/can not accept such object), when d&d-mode cursor is passed to the window?

http://www.chromeplugins.org/google/chrome-tips-tricks/drag-drop-tabs-firefox-google-chrome-7256.html - they can be accepted in Chrome, receiving the URL. No plugins involved.