Rounded, sausage-shaped tabs, buttons, and input fields, all drenched in vomit-inducing purple and magenta - the very best of modern design trends. It's really sad to see Firefox turning into yet another unoriginal garbage desperately trying to blend...
I also really miss this feature. At the moment, I have to use the Firefox Multi-Account Containers extension just to be able to reorder the container list, even though I don't really need any of the additional features the extension provides.