Thanks for the review and the feedback! I will keep in mind your point about the buttons being too small and the preference for less color.

The sidebar can be controlled (to a certain extent) in Tab Stash's preferences. However there are some situations (e.g. on an extension update) where Firefox will just decide to open the sidebar and the add-on has no control over this.

Hope this helps, and I'm glad to hear you're enjoying it!