This isn't a new bug. It's the same bug from the previous stable GMS 1.4 release, still unfixed apparently. Box2d doesn't run in HTML5, although it worked fine in much earlier versions.
This was reported and discussed before. HTML5 throws an "undefined variable" error upon initializing the physics world, and then freezes.
This was acknowledged by Daniel Cleaton on the Mantis system. It was said to be "fixed internally" and waiting for a new release. Unfortunately, this latest release still appears to have the same bug.
The good news is that Box2d runs fine under HTML5 in the EA version (and in Studio 2, of course).