As promised, the update on changes in Firefox 73 is short: There is a new sidebarAction.toggle API that will allow you to open and close the sidebar. It requires being called from a user action, such as a context menu or click handler. The sidebar toggle was brought to you by Mélanie Chauvel. Thanks for your contribution, Mélanie!
On the backend, we fixed a bug that caused tabs.onCreated and tabs.onUpdated events to be fired out-of-order.
We have also added more more documentation on changing preferences for managing settings values with experimental WebExtensions APIs. As a quick note, you will need to set the preference extensions.experiments.enabled to true to enable experimental WebExtensions APIs starting with Firefox 74.
That’s all there is to see for Firefox 73. We’ll be back in a few weeks to highlight changes in Firefox 74.