It's disabled by default, but I had no idea this was added.
Firefox mobile users started noticing something peculiar this week when sharing links to WhatsApp. After hitting that share button, their messages were getting an unexpected tagline: “Sent from Firefox 🦊” with a direct link to the Mozilla app store listing.
The feature appeared quietly, with no fanfare or announcement from Mozilla.
https://piunikaweb.com/2025/11/26/sent-from-firefox-whatsapp-share-signature/
That happened to me yesterday. Fucking embarrassing to accidentally spam a work colleague like that.
I certainly didn't enable that option. Are you sure it was off by default?
Edit: I was enrolled in "Studies", that one has a study active, for testing the spam. Guess I won't help with their studies anymore.