After moving a frame using drag and drop, the wrong frame is selected (Firefox)

[juliandescottes]

Steps to reproduce :

• open Piskel in Firefox
• open a piskel with 4 distinct frame
• using the mouse/drag-and-drop, move the first frame to the another position

Expected : the moved frame should be selected
Actual : the new 'first' frame gets selected.

Some investigation :
We have a moved frame F, going from index i1 to i2.
After the mouseup releasing F, the currentFrame is set to the new index of F, which is i2 At the next call of the render loop, all UIs will redraw accordingly.
However on Firefox a click event is also fired after the mouseup event, which triggers another call to setCurrentFrame. This one is based on the data-attribute of the event target. Since the UI has most likely not had time to redraw yet, F's data-attribute is still i1.

Could be a bug/limitation of jquery's sortable util.

[juliandescottes]

Fixed by @zoeesilcock