What I did:

1. Tried to open the sidebar from a click event
2. Tried to get the background page from a click event
3. Tried to open a new tab from a click event

What happens:

1. browser.sidebarAction is undefined.
2. browser.runtime.getBackgroundPage is not a function.
3. browser.tabs is undefined.

What I expected:

1. The sidebar to open.
2. An alert showing a message stored in main.js.
3. A new tab loading mozilla.org to open.