Downloads won't open

Use mozilla on my work computer I do a lot of my work from nnanet.com which is nissan's internal website. A lot of the things in there once the form is filled out you hit submit and it used to put the form into the download section and pop it up so it could be printed filled out. since about two weeks ago it doesn't work at all. the docs go to the download folder but can't be opened any longer. They all work fine on internet explorer. Nothing has changed, same computer, same programs, I am the only one who uses this computer. Any ideas?