It only works if you're dragging a tab into another tab area.
You can't drag a tab into window without tabs (only 1 tab hence no tab area). You also cannot drag a window (only 1 tab) into another window.
FF does have some subset of Chrome's functionality, but you cannot use it like Tab Candy to easily organize sets of tabs. Which is the whole point of the post.
Firefox and Chrome have the exact same functionality here, unless you turn off "Always show the tab bar" in the Firefox prefs. (It is turned on by default in Firefox 3.5 and later.)
You can't drag a tab into window without tabs (only 1 tab hence no tab area). You also cannot drag a window (only 1 tab) into another window.
FF does have some subset of Chrome's functionality, but you cannot use it like Tab Candy to easily organize sets of tabs. Which is the whole point of the post.