While the idea is great, I unfortunately had to deactivate the add-on for now, since I cannot find any setting to tell it, to only open on pdf documents either by individual user choice or by somehow detecting an academic or even a journalistic outlet first. I don't want this plugin to always open with the entire overlay over any pdf I happen to open online! It would also be nice if on top of that it wouldn't automatically choose the download folder and instead would let me choose the one I actually want, as per my actual default browser setting!

Thanks for your attention.

i cant use when click pdf button at scijournals.onlinelibrary.wiley.com

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.