title: How to create a sidebar with Firefox WebExtensions?
body: <p>I'm trying to migrate an extension and yes, I know that I can not add more than one button per <a href="https://developer.mozilla.org/en-US/Add-ons/WebExtensions" rel="nofollow noreferrer">WebExtension</a> to the browser interface, but I would like to know if it is possible to create a sidebar somehow. I know that I can manipulate the DOM of the site, but in some cases (e.g. Facebook) it is difficult due to their css, and I need to make sure that my sidebar is visible from any Website where the user wants to use it to see some stats. </p>
  
  <p>Do you know a way for creating a pseudo-sidear (DOM), no matter the site?</p>
  
  <p>PS: Do you think a sidebar (browser UI) will be available in the future?</p>
  
  <p>Any idea is welcome,</p>