Five years after the appearance of the already familiar and almost native design, Mozilla, along with the release of Firefox 48 (scheduled for August 2, 2016), plans to update the design on
addons.mozilla.org .
However, there are no major changes in this update, a slight change in styles, colors, as well as the use of adaptive styles from the Firefox for iOS website.
Future appearance of AMO (screenshot from Mozilla
blog entry ):

Already, you can use the
script for
Stylish to see what the new AMO looks like and send a
pull request in case of detection of artifacts.
In a Mozilla blog, the author says that all design changes were made in a live way by means of Firefox Page Inspector.
Also in the note it is said that this is the first of many steps aimed at improving the user experience for installing add-ons in the browser, and for developers. In general, about the new design speak positively.