Run GtkLauncher https://bitbucket.org and go to "Log in".
The log in form appears but the browser becomes unresponsive, leaving you no option but to kill it.
This was reproduced with WebKitGTK+ 2.4.9. The latest stable version (2.8.3) does not seem to be affected by this.
This is very old and seems to be working now, so I'm closing it.