Fira is a beautiful destination and easy to get around.
We took the cable car up to the top then the bus to OIA. This is a lovely town to walk around but in peak holiday period, very difficult to leave as the busses are filled very quickly with pushing people. THe bus companies have no system when it comes to boarding or departing the bus and it becomes a very dangerous exercise. Time for them to put in a queue system and to stop the pushing and shoving.
Often if there are several ships tendered, the line to the cable car can be extremely long. The alternative is to walk down the donkey track which takes about 1/2 an hour. be warned that the track is slippery and extremely smelly.