Not sure why OP linked to a fork instead of the original. But the original has a bookmarklet version if you would prefer an alternative.
https://github.com/jswanner/DontF-WithPaste?tab=readme-ov-fi...
https://github.com/jswanner/DontF-WithPaste?tab=readme-ov-fi...
[0] https://addons.mozilla.org/en-US/firefox/addon/don-t-fuck-wi...