Where is option to change PDF download or preview settings in Firefox ?

I am idiot enough to not to find settings or option where I can set my firefox to download PDF files instead of opening them in browser. It will be even better if there is choice to ask to download or to open directly in browser. I am sure it it there in firefox but just can't find it.. Please be exact to let me know where I can change it or we need to have a plugin to do this ? But I think firefox is mature enough to have this built in ?

PS: I am running Firefox 40.0.3 .. (hell.. I never realized that Firefox has reached version 40 already ).

Nevermind, I just figured it out myself. For anyone else who may need , its in
Settings --> Options --> Application
There type "PDF" in bar, it will show application dealing with PDF, set it to download or preview or "Always Ask".

So it is exactly I wanted.