How do I return to getting the option to open a PDF file vs automatically going to the save option?

When selecting a PDF file from the web, I was getting a pop up box that asked if I wanted to open the file or if I wanted to save the file.  Somehow I am not getting this pop up box anymore.  When I select a PDF file, it automatically goes to the save file option.  I want to have the option to just open the file before making the decision to save it.  How do I make this happen?