What does Fast Down Button look like on Facebook?

On Facebook it is the design shipped in 16.0, shown above at full size. Older revisions are listed beneath it.

When did Facebook add Fast Down Button?

Facebook first drew Fast Down Button in 2.0, released February 20, 2017.

Meta Platforms, Inc. has shipped 12 versions of Fast Down Button. Each is dated, so you can see when the design changed.

Facebook 4.0

Facebook shipped a new design for Fast Down Button in 4.0, released April 1, 2019. The previous design is shown beside it.

✳ marks a release that redrew this emoji. The rest re-shipped the design unchanged.

What does Fast Down Button look like on Facebook?: On Facebook it is the design shipped in 16.0, shown above at full size. Older revisions are listed beneath it.
When did Facebook add Fast Down Button?: Facebook first drew Fast Down Button in 2.0, released February 20, 2017.
How many times has Facebook redrawn Fast Down Button?: Meta Platforms, Inc. has shipped 12 versions of Fast Down Button. Each is dated, so you can see when the design changed.