I hear what you say. Sorry to say -
However I did experienced that ref. version probably didn't update properly. After 50 years (I don't fool you) in IT sphere there is one thing I hate most of all; not having control of any kind of updates. (My fault not to stop auto update as I noticed that autoupdate...exe was removed from the installer folder). It's now set a stop in the Settings.
The last automatic update did not show up any pdf sections in the Settings, killed my password bank, neutralized automatic storing of new password, neutralized automatic fill in name, addr, etc.
When installing PDF viewer I was asked what local viewer I used. Typed that. When going into the Settings again, then I found the PDF option. I have one and only one addon. There were no Q's ab double installation !!
Rollbacking the last recovery; I restored all former misery except of one thing - PDF addon was gone. Then I had to reinstall the addon once again and to my surprise ir works perfect, no download window.
What actually happened, only heaven knows. What I do know after taking control my system works as I expected.
(except for one thing JW Player is only working if I play the video in a new tag, never directly from the source tag.