First view your .pdf file with firefox. Then at opening select the "Better view" in the top the page and choose your pdf file viewer software. It is more easy then firefox pdf viewer.

sorry, it's not the pdf's in firefox/ on the internet, it's the pdfs already on my pc (in my documents, etc.). They won't open normally.

Try this:

1. Right click your PDFs, click Properties
2. Go to the General tab
3. In the Opens with section, click the Change button
4. Select Adobe Reader (or Foxit Reader/Whatever PDF viewer you use)
5. Click Apply then OK.

Does it work then?

Thanks moses! that fixed it. Don't know why it did it to begin with, but it's fixed now.

This happened to me as well. You need to reassign Adobe Acrobat or Adobe Reader as the default PDF handler...

Open up Adobe Reader (not Acrobat, if you have it on your system); go to "Edit", "Preferences", "General"; at the bottom of the General settings screen to the right "Select Default PDF Handler"; pull down and choose the PDF handler (e.g., Adobe Acrobat or Adobe Reader).

The other options described above and in other threads did not fix the problem for me.

Hi. I had this problem myself two times no, it`s not a problem to fix this as I just change it to adobe reader. But why does this keep on happening? is there a way to prevent it?