The Mekorama on the Web feature does not seem to be launching anything for me. I noticed it Friday (2023/12/29) evening. It gets to about 90-95% and stalls there. I believe I played a level Thursday, just the day before. I hope this is the appropriate avenue for reporting this.
Okay, made contact with Martin Magni. He said thanks for the report, they're working on it now. In the meantime, if you go to play.mekorama.com and play the first story (tutorial) level, then you can load and play levels from the forum.
@Shroomir Thanks. It looks like that happens only with Firefox on Windows. Is that what you are using? It works with Chrome on Windows.