Hi, sorry for the late reply. Here is a new addon where you can choose any web (any URL) to pin: https://addons.mozilla.org/es/firefox/addon/pinned-any-web/

Hi and thanks for using my addon!

What the add-on does is simply to load the URL www.messenger.com into a pinned tab. Everything else is the same as a normal Firefox tab. So, the video autoplay is a setting from messenger itslef.

Hi and thanks for using my addon!

What the add-on does is simply to load the URL www.messenger.com into a pinned tab. Everything else is the same as a normal Firefox tab. So, the dark mode is a setting from messenger itslef.

Hi and thanks for using my addon!

What the add-on does is simply to load the URL messenger.com into a pinned tab. Everything else, is the same as a normal Firefox tab.

If you try to load that URL in a normal Firefox tab and loads fine, then the add-on should works fine. If it doesn't loads in Firefox, then you should have some problems with Firefox itself.