Thank you for following up! It’s funny, when I edit the experiment you shared above (https://farm.pcibex.net/r/ldGLsD/) and upload PennController 2.1 beta to the Modules folder and then test it on Firefox, everything just runs smoothly: I don’t experience any preloading time and the videos play back normally. It’s actually when I don’t upgrade to 2.1 beta that I experience preloading times. This will be hard to troubleshoot…
Anyway, happy new year to you too!