When hovering over the back button, a faint circle is visible around the arrow icon, which is an artifact from the default Firefox theme. (This can be demonstrated by changing "Density" to "Compact" in the Customize menu; the circle stops appearing since it is not part of the back button with that density.)
Obviously this circle is not a part of the Adwaita styling, and should be removed if possible.
Oh I see. I recently refactored this part of code (#36), I changed a lot of selectors and they actually work nicer now, but I guess the circle came back and I didn't notice it. Thanks, I'll fix it soon.
When hovering over the back button, a faint circle is visible around the arrow icon, which is an artifact from the default Firefox theme. (This can be demonstrated by changing "Density" to "Compact" in the Customize menu; the circle stops appearing since it is not part of the back button with that density.) Obviously this circle is not a part of the Adwaita styling, and should be removed if possible.