Currently, when an add-on is installed, a doorhanger is shown pointing to the hamburger menu button. I think it would be less confusing if the doorhanger could point to the browserAction for the add-on, if one is available on the toolbar. That will help the user find the main entry point to the add-on.

(An alternative that would serve a similar purpose would be to allow add-ons to show their own doorhanger upon installation. Currently this is not permitted.)

I've investigated this and there are a couple issues. One is timing doesn't work, the extension typically loads after the panel is shown. The other is that there are a number of panel problems related to install that need to be addressed in bug 1568635, and until that is done, making this change could result in a bunch of complications. I think this has to wait until we can address bug 1568635.

Can we live without this change for now?

I do think it would be useful to have this, not just for the Secure Proxy but also for other add-ons. Markus, do you have an opinion on this?

Placing the doorhanger on the extension icon (if there is one) was the original intent. So I would love if we can make that work.
I think we went for the Firefox menu as a first iteration, but then never iterated on it again.
Here is an old mock showing that placement: https://bug1264239.bmoattachments.org/attachment.cgi?id=8740871
(I couldn't find the bug dealing with the actual implementation of that confirmation.)

To even better integrate, instead of allowing extensions to do their own doorhanger, we were thinking to allow for a section of our install confirmation to display content specified by the extension.
Here is an old mock of how that could look: https://mozilla.invisionapp.com/d/main#/console/7542912/161497216/preview