Thanks a lot ! The issue is not the opening of the modal, it opens on both. The issue is, into the modal, when clicking on the big PDF icon, the PDF file opens in another window in v0.7.0, and nothing happens in v0.8.4. This issue is only in Firefox, it works on other browsers.
But, thanks about the click_window option : I've changed it, and the PDF opens directly in another window, without the modal step.
Problem solved, thanks !