Just discovered why I'm seeing quoted Mastodon posts.
It's not mastodon.social that added quoted posts.
It's not Firefox that added quoted posts.
It's the Graze for Mastodon extension that added it.
So there we have it! Graze for Mastodon just added quoted posts to Mastodon!
Wow! That was a lot of excitement!
By the way, I originally installed Graze so I could like and boost posts from remote Mastodon servers.
I didn't expect them to add a quote feature.
But I'm glad they added a quote feature because it actually displays really well, and it makes for a much better Mastodon experience.
Still, it would be nice if Mastodon has native support for quotes.