b5796e10bf
I ended up having to change some of the fundamentals of the popupnotification element because the code relied on being able to inherit inline event handler attributes such as buttoncommand as oncommand on the button element and so on. The primary user of the popupnotification element seems to be `PopupNotifications`. Following a pre-existing coupling with `PopupNotifications._onCheckboxCommand`, by default all commands/actions will simply call the corresponding `PopupNotifications` handler. However, I found at least one instance in `panelUI.js` that tries to override the command handlers. I solved this by dispatching a custom cancelable event on the popupnotification element. Differential Revision: https://phabricator.services.mozilla.com/D231927