How To: Always open PDF documents in your browser
For many users, it is more comfortable to always open a PDF document in their browser.
To set your preferred browser as the standard app for viewing PDF documents, right-click a PDF on your computer (e.g. on your desktop) and select "Open with", then "Choose another app":

A dialogue window opens in which you can select the standard app for this file type:

Select your browser (if it's not listed, click "More apps") and set the checkbox "Always use..." active.
You can always change this setting by right-clicking a PDF document.