Steps to reproduce:
it should take a fraction of a second to open the editing interface, and it should be in a new clean page, not a stupid popup-like draggable overlay which only makes sense for small amount of lines. Or at the very least, if it must be in a popup (because popup/ajax is always cooler for its own sake, apparently), then it should be correctly positioned within the window, fast to load, usable, and you shouldn't need to scroll the containing page to view the whole popup (which has its own scroller inside).
It opens in a fancy popup-like draggable overlay, which is ridiculously ill-positioned (starting near to the bottom of the current window), so that you have to scroll the containing page in order to see the whole popup, which in turn has its own scroller (the latter being ok). The popup should be positioned fixed to the viewport, not to the page.
Also, the popup is awfully slow to drag.
This is a regression. The old style interface, where editing rows would lead to a new fresh window rather than open a popup, was FAR more usable.
The new everything-in-fancy-ajax-popups-at-all-costs way of doing things is a huge step backwards.
In cases like this, the popup should not exist: the editing interface should open in a new page, taking all the necessary precautions so that you could go back to the previous page with the browser "back" button. That is possible.
Unless the popup can be made decent, clean, usable and functional, which it definitely is not, currently.
Just one more case in which usability is being unnecessarily sacrificed in favour of (questionable) aesthetics.