Force browser to open file instead of prompting download

Question

When clicking a PDF link in Firefox and Chrome, the file will sometimes be opened for in-browser viewing and sometimes prompt a \"Save as\" dialog.

If I wanted to force

Answer 1

You can achieve that by setting the appropriate header (for instance, in case of PDF, the header will be Content-type: application/pdf;

With this header, the browser will know the mime-type of the file and display it if it is compatible with it.

Here you can see the headers for a PDF.
As a hint, what I like to do is to use some sort of controller (in case you are using a backend language) that handles the download. Hence, to download myNewProject.pdf I do

Download!

Then I can set the appropriate headers depending on the file type, or if I want to force download or view it in the browser...