It has taken a long time for the Firefox team to come up with a significant update to the Add-ons Manager, but it’s finally coming to Firefox.next. It looks and works great and there are a lot of opportunities for the new interface.
The Add-ons Manager as you knew it is gone. The new version works in a tab with a sidebar to choose what kinds of add-ons you want to work with: Languages, Extensions, Themes, and Plugins. Plus the Get Add-ons section that integrates with Mozilla Add-ons (not hooked yet) for the fastest, easiest experience.