There's nothing "simple" about this extension. It's complex and mostly confusing. Here are a few suggestions:
- Have default groups coincide with native multi-account containers.
- Clean the dropdown menu to choose group. It's so busy it's not usable.
- Create sane defaults and avoid three pages of settings at all costs.

In other words: design the UX yourself, don't defer this design to users putting every imaginable option under the sun everywhere.