How to access the search bar in a Firefox 57+ ("Quantum") web extension

Question

I try to write my very first webextension, following this tutorial. I wrote a manifest.json and added a background script as I want to provide global functionality: I want to clear the search bar once the search was performed - basically it's this, but for Firefox 57+.

My question: How can I access the search bar at all?

I found a list of available APIs, including the tabs, the menus, and so on, but no search bar...

Answer 1

I filed a bug request as @Smile4ever suggested, which was declined yesterday. The extension team suggested to file a feature request for what "my" extension should have done, but from the perspective of this question: It is and will not be possible to access the search bar from an extension.