open webkit, copy/paste http://o3d.googlecode.com/svn/trunk/samples/stencil_example.html into first tab. Open a new tab with apple-T, click on a bookmark or navigate to a url, wait for page to load. Click back to first tab - boom, safari crashes & everything else too.
This is almost certainly a problem with the third-party plug-in that the URL you have provided requires. I do not have that plug-in installed and I am unable to reproduce the issue that you describe. You should report this issue to the developer of the plug-in.
Agh, sorry - forgot it was using a plugin. Closing as invalid.