Its good that firefox has vertical tabs now but I think it could improved more if we could scroll on the vertical tabs to change tabs just like Sideberry extension which supports this.
I would like this feature. And to be clear, I would like to use CTRL + scroll to change tabs, not just scroll alone. There is already an about:config setting, "toolkit.tabbox.switchByScrolling", which when turned on causes scrolling alone to switch tabs. But this takes away the ability to scroll up and down the actual vertical tabs panel (Yes, sometimes there are enough tabs open to warrant this, and it is FF's default behavior when toolkit.tabbox.switchByScrolling is not turned on).