Fixed.

Drag and drop does not seem to be slow on FireFox. Perhaps the change to the 'trunk' version of jQuery UI helped.

To determine if the slow speed is due to repeated calls of the orderable finder function within the Reorderer, I placed a console.debug() at the top of that function to print out whenever it is called. I tested with Lightbox.html.

WIth respect to drag-and-drop, the orderable finder function is called once, ever. It is called from Reorderer._enableDragAndDrop().

(With respect to the keyboard, the finder function is called every time a cursor key is pressed, regardless of whether it is for navigation or moving a thumbnail. See http://issues.fluidproject.org/browse/FLUID-113).

Downgraded to critical – still intend to fix for release 0.1, but no longer a blocker.

As a test to see if getting rid of images will be quicker, I hooked up the Reorderer to our "grid-big.html" abstract example. This is a large grid of 1000 orderables. They are essentially <div>'s simliar to those in the Lightbox.html, but without any images. Loading the page into FF on a Mac led to a spinning beach ball for about 30 seconds, followed by an alert that says "unresponsive" script.

Short conclusion: our current dnd does not scale.

Hypothesis: it's the way we build the "selector" to hand to the 'accept' option to jQuery().droppable(). That is a string of 1000 id's separated by a comma. Now, since we know exactly which elements are the droppables, why can we not pass an array to jQuery().droppable()? Why must it be something that requires jQuery() to figure that out again?