(Only on Firefox) Why links to pdfs on my website ask me whether I want to save file?

The two pages of my website can be found here:
https://www.lightfigures.com/metaphysical-diaries/
https://www.lightfigures.com/spiritual-diaries/

For some reason, and only on Mozilla Firefox (not Explorer or my Tablet) when I click on the links that should bring up pdf files, I am shown a save the file dialogue box. This only happened recently when i made some changes to the WordPress specs, but these changes did not have on effect on other browsers. Any help here would be really appreciated! Thanks,

-Charles