It does work somewhat, but it is not giving me notification anywhere about the Beall listed journals. The website feature request and bug report points to the now dead Google Plus. I can't find the source code, that I think it would be nice to be on GitHub.
It's a nice project, but it seems currently unmaintained.

Very handy for searching full articles.
Thanks to the author!
Очень удобно, для поиска полных статей.
Автору спасибо!

it does not work.

I am glad this add on is back! Thanks!

Not working for me.

A fantastic add-on for researchers, thanks so much for saving me time on searching full-text