Sadly it doesn't work anymore, but there are already alternatives as mentioned in other comments.

As of Jan 2023 it no longer works.

Sadly, this one doesn't work anymore.
You can use "Lap Clipboard Inserter" instead.

You can find a fork of this extension “Lap Clipboard Inserter” that fix deprecated execCommand”

worked just fine until 16/11/2022.
No Idea what happened ever since then, but no lines/contents are displayed anymore.

It works, but it's very bland and like the review below says it's not nearly as good as Clipboard History Pro on Chrome. Sad it's not available on Firefox.

Kein Vergleich zu Clipboard Histoy Pro aus Chrome. Ich finde hier keine kopierten Texte. Deinstalliert

LOVE this, can NOT live without now!!!

It works fine