Description of problem:
In Fedora 21 I can easily throw the mouse cursor against the right screen edge and grab the scrollbar of a maximized Firefox. But in Fedora 22, this is not possible, the scrollbar does not 'extend' to the very edge. Instead, I need to move the cursor 1 px from the edge in order to grab the scrollbar. It seems there's a 1 px border between the scrollbar widget and the screen edge that acts like a blind spot.

The end result is that with GTK3 Firefox you can no longer easily grab the scrollbar without thinking, just by going to the very right and clicking on it, but you need to be more precise and looking at the cursor position. Which is, of course, not optimal.

Version-Release number of selected component (if applicable):
firefox-38.0.5-2.fc22.x86_64
gtk3-3.16.3-1.fc22.x86_64

How reproducible:
always

Steps to Reproduce:
1. maximize firefox, open a long page showing scrollbar
2. mouse the cursor to the very right, touching the screen edge
3. click to grab the scrollbar, nothing happens
4. move the cursor 1px to the left, click to grab the scrollbar, it works now