Toolbar in compact mode (all good):
Toolbar in non-compact mode (the forward arrow appears narrower in comparison to the back arrow):
I noticed that this issue is more pronounced when having Orion window positioned on an external display. This manifested on a 3440x1440 non-HiDPI display so that may be a factor.
On Macbook's Retina display the non-compact toolbar appearance seems fine, as seen in the screenshot below: