Sometimes custom clients run when the normal client does not...
While the Haven & Hearth client is listed as open source, I'll warn that not all modifications should be trusted. The particular one linked to you above is one of the ones that the community has accepted. You can find other clients and mods in "The Wizards' Tower."
As for a crash report, you'll need to search your hard drive for a file called "hs_err_pid.log." This is usually in the Java directories somewhere, but not always (can be set by the developer.)
Good chance you have a graphics device error. What hardware are you using and software? Odds are you have gotten the 32-bit build of Java instead of 64-bit (due to the browser you're using). If you make sure you install Java 8.x 64-bit build, it may fix the problem without digging for the crash log. The
download link. Make sure to uninstall any current versions of Java and then reboot your computer first.
Opinions expressed in this statement are the authors alone and in no way reflect on the game development values of the actual developers.