Ciao!
Yes, it is much easier now because there is one company across all buses/trams in the region.
Here is the website on the AT bus company website that explains the tickets -
https://www.at-bus.it/en/ticket
but it basically boils down to this:
--> if you're traveling WITHIN a city, you use the URBANO ticket. Both Florence and Pisa are main towns in their province, so they use the URBANO capoluogo ticket which costs 1.70 euro (you can see the list of towns listed)
--> if you're traveling BETWEEN cities, you use the EXTRAURBANO ticket.
You cannot buy the 10 tickets that are a mix of urbano and extraurbano, so it might make more sense to buy tickets as you need them. The savings of buying the carnet of 10 tickets is quite small.
The website has a trip planner that will tell you what buses to take between your destinations.
Between Pisa and Florence, I would actually suggest taking the TRAIN - there are trains from SMN in Florence to Pisa Centrale every half hour and take about an hour, they do cost more around 10 euros but buses take over 2 hours, so it is faster to take the train.
So you can buy urbano tickets to use within Florence or within Pisa, then use the train to move between Florence and Pisa.