Make vertical scroll wheel on a mouse scroll horizontal tabs without holding down the shift key.
With the “see website titles in tabs” option checked, horizontal tabs overflow easily. As a mouse user with many tabs, this would be a huge QOL improvement. In clamshell mode, I do not have access to MacBook’s trackpad. Having to hold down the shift key while browsing with the mouse with one hand is very inconvenient and disruptive. Firefox implements this and it works very well.
Edit: I found a locked post with the same suggestion but no conclusion here.