Some extensions require to open sidebars automatically based on the URL the user is on or other criteria. See https://addons.mozilla.org/firefox/addon/mdn-documentation-tester for example. Therefore, there should be a way to toggle sidebars from within the extension. This could either happen via a manifest property holding a regular expression for URL-matching, or, to be more flexible, via an API like in the Add-on SDK. Sebastian  https://developer.mozilla.org/en-US/Add-ons/SDK/Low-Level_APIs/ui_sidebar
Created attachment 8844117 [details] WebNotification-Options.PNG This seams to be very powerful, and potentially annoying for people. And it seams that the example could well work without the sidebar being opened automatically. If we intend to do this, it should be an optional permission that the user has to grant once before the sidebar can be opened, and an option to easily revoke that permissions from the open sidebar. Similar to how we implemented Web Notifications - see attachment.