How to reproduce:
1. Download the attached project
2. Enable exception support under Player settings
3. Build the project for WebGL using the menu item Aquiris -> Build -> WebGL (Debug)
4. Open it with 64bit browser (I checked with FirefoxDeveloperEdition)
5. Play as a guest (project can crash at that time) or play the game further (it can crash after you kill some enemies or after reloading the game)

Note: WebPlayer build works great.
Also sometimes I get the crash with abort() or due to unresponsive script all browser crashes.