This one contains logic only, it could be moved to a simple JS module.

https://searchfox.org/mozilla-central/source/browser/base/content/urlbarBindings.xml#2752

Seems like most of the logic could be folded in here: https://searchfox.org/mozilla-central/source/browser/base/content/browser-addons.js#35 ?

(In reply to Tim Nguyen :ntim from comment #1)

Seems like most of the logic could be folded in here: https://searchfox.org/mozilla-central/source/browser/base/content/browser-addons.js#35 ?

I'm looking into making this a customized custom element in Bug 1487065 - work in progress at https://hg.mozilla.org/try/rev/6676100706fd87ee632d076d4c4f9e5c72aca33e#l1.2. If someone wanted to handle this directly in js at browser-addons.js that would be great as well. The trick will be hooking into the right time to run construction and destruction logic, I think. Perhaps PopupNotifications.jsm would emit a notification we could listen to.

This UI can be seen when installing an addon, like at https://perf-html.io/. It's the step that shows download progress.

This was done as part of the popupnotification conversion (Bug 1487065)