Just published my game (announced here).
The game focus and extenal URL problems are still there, but I wanted to mention that I solved all the audio caching problems replacing the latest soundmanager.js and soundtools.js in the export build with the ones included in v3.6.80 and removing the Howler call in the index.html file.
I know maybe it’s not the optimal solution (I replaced the new sound system with the old), but that way the game takes around 30 secs less to start (no precaching needed) and the general performance seems the same. I kept the precaching scene in the published version just in case.