Hello,

    * What led up to the situation?

          I went to https://youtube.com/ using the address bar.

    * What was the outcome of this action?

         Firefox displayed a recommandation (an ad) for a non-free
extension: "Enhancer for YouTube™".
         An blue icon appeared at the right of the address bar. Upon
click, a bubble invites the user
         to install the extension without any warning on the license of
the extension.

         The addon page says "Custom license".
         The license says: "The Developer grants You the right to use
Enhancer for YouTube™ with any of the compatible Google Services"
         And: "Except Authorized Persons, nobody has the right to
distribute Enhancer for YouTube"
	And also: "Except where otherwise noted, and except Authorized Persons,
nobody (i) has the right to reverse-engineer, modify, reproduce, copy,
duplicate, or use any part of the Source Code without The Developer's
consent, neither "as-is" nor modified; (ii) has the right to distribute
or in any way expose the Source Code over the web without The
Developer's consent. All rights not expressly granted to You are
retained by The Developer."

    * What outcome did you expect instead?

         I expected Firefox as shipped in Debian not to spontaneously
recommand (show an intrusive ad) for a non-free extension.
         Until now, I trusted Firefox and its UI to provide good advice
to users.

    * Addons currently installed on my profile:
         - ADB Helper
         - Grammalecte
         - I don't care about cookies
         - KDE Connect
         - Plasma Integration
         - Save Tabs
         - Tree Style Tabs
         - uBlock Origin
         - uMatrix (disabled)

     I cannot seem to reproduce the issue on my current profile or a new
profile.
     I do have a screenshot if needed.