* Move the chrome panel buttons into a `box` which is inserted into #navigator-toolbox
* Adjust what open/closed means using hidden instead
* Capture a weak ref to the focused element on open, and attempt to put focus back on exit
* Add some restore-focus tests
* Fix a bug where cancel via overlay "X" button wasn't exiting properly
* Place initial focus in the preview dialog button on the download button
Differential Revision: https://phabricator.services.mozilla.com/D181184
e1e878dc76