Some Java applets are able to slow down Firefox to the extent that visiting other sites in the browser (in other tabs) will not work. One method to reproduce: 1. Go to: http://www.izhuk.com/painter/ 2. Open other some other sites in another window or tab. Result: The other pages will not load for some time (I did not actually wait to see how long it would take for things to become responsive). Closing Firefox crashes the browser due to another bug.

From the limited information given by the reporter this appears to be a duplicate of another bug related to Java/Memory Leaks causing lag and crashes. Sound similar to Bug 275783 going to go ahead and dupe. CCed myself *** This bug has been marked as a duplicate of 275783 ***