I've been trying to figure this out. On the PC I am supposed to set favourites 1-8 (I think) but how do I actually do this? I tried holding down the 1 key while mousing over but that didn't work. I'm clueless.

Okay so go over an item you want to favourite and press F.
Come out of that window.
Open your favourites window (Q) and then however your mouse over one of the favourites.
Press a number 1-8 while hovering over them.

You can now use that number as a keybind to quickly activate what it was.

So MANY thanks for that! Finally

Also something I noticed thats kinda wierd if you rebind the toggle viewpoint (1st / 3rd person) to a differant button other than F you have to use that button to set the favs in the inventory list but the UI thing at the bottom will still say push F to set as fav. This messed me up for awhile until I realized that I had rebound to toggle view button to U.