This addon is great for me since it has the option to scroll between tabs using the mouse wheel. Didn't realize how comfortable this option is until I lost it.

What would make this addon absolutely perfect, would be a shortcut button (F1 for example) or the ability to set it ourselves. Would be much faster to switch sidebars this way.
Plus, a built in dark theme would've saved me some time, and I'm sure there are many others who would've appreciated that. Although the customization options are very good.

2 tiny things that slightly bother me; Scrolling between tabs isn't smooth, it even gets kind of stuck sometimes + When I hide the groups on the side, it doesn't always stay that way (every time I restart the browser).

Other than that it's great. Greatly enhances my browsing.

EDIT:
Both of my major complaints were fixed. Great job!