TabDragging

Currently our tab dragging behaviour isn't very good.

Here are a few of the problems:

• There is a confusing drag cancel animation that happens on OS X (Bug 504847)
• When you drag a tab around the desktop on Windows it appears as though you dragging onto the desktop, but you're actually not. Other browsers don't do this. This is probably because we're setting the type of the data object being dragged to a URI or something similar, and the icons on the desktop try to react to it (folders will accept URIs by creating web shortcuts inside them, and application shortcuts accept it by trying to open the application with the URI argument, but of course none of these things happen in reality.)
• Dragging doesn't actually move the tab it just moves an image of the tab and you get indicators. I think every one agrees that behaviour in Chrome and Safari is better here. Specifically, what Safari does (moving the actual tabs around when you're dragging onto the tab bar itself, and then changing to a window when you drag out of the tab bar) looks like a sane behavior. We would probably want Chrome's tab-like preview image which moves with your mouse pointer as well.
• There's no good feedback when you release the tab. Chrome and Safari both have pretty animations (Bug 466196)
• In multi-monitor setups, when you drag a tab from the application window in the first screen and release it onto the second screen, it probably means that you want the new window to be created on the second screen. It's created on the same screen as the application window, however.

A bunch of these problems are the result of using the drag & drop service from the OS. To solve them we should probably avoid using it. This will give us more flexibility and will avoid the negative interaction problems.

Possibly related sprint: Visual Affordance for Tear Off Tabs