Issue reproduced on Ubuntu with OpenGL enabled.
Happens on an url using graphic acceleration, for example : http://get.webgl.org

Issue is that the TextureMapperGL created a GraphicsContext3D using the current OpenGL context. This is done by storing a reference on QOpenGLContext::currentContext() inside GraphicsContext3DPrivate::GraphicsContext3DPrivate().
When exiting QtTestBrowser, Qt releases QOpenGLContext before the release of the GraphicsContext3D in webkit which leads to a crash when destoying GraphicsContext3DPrivate.

Log attached showing the destruction of the QOpenGLContexts and the access to the freed context from qtwebkit.