Hi Andrei,
Presently, the Permission view (.../Admin/Security/Permissions) is an html table and has no scroll bars. If you have more than 7 or 8 Customer Roles then there is no way to assign permissions to anything off to the right that is beyond the resolution available. Even clicking and dragging the mouse doesn't work.
Please wrap the table with a scroll div.
<div style="overflow:scroll;">
<table class="table table-hover table-bordered">
....
</div>
Also, congrats on nop 3.9 beta!
Thank you
Charles