They should tell you in advance if the tour your are buying (day and time) can include the dome on the inside or not. I did read that if the dome was closed, the guide would just show you the outside but literally after the tour, the dome opened so they should warn you. Although the guide was awesome.
Eleonora made our Florence visit very entertaining as well as informative. She has a good spoken voice and was very knowledgeable about Florence. Highly recommended.