most (not all, some contributions are QTVR-only due to historical reasons)
many, but depends on photographer's choice of file upload (newer event = more likely to work) and your device's capabilities. You may experience slow playback, distorted images or unexpected browser quitting if there is only limited memory/GPU power available.
This pan may not be my best work for full screen display but this pan of mine from mexico is one I love to look at the most. (especially living in Vancouver, actually had a tough time deciding from the all the beach pans). Hope to head back to Tulum soon!