It was reported at
http://defect.opensolaris.org/bz/show_bug.cgi?id=13508

See comment #27 for reproduce steps:

Jürgen Keil 2009-12-27 09:04:24 UTC
I'm now able to hang firefox on the amd64 machine, too:

- disable cpu core 1 ("psradm -f 1"), so that the system runs with
  exactly one core

- open s10 download page


https://cds.sun.com/is-bin/INTERSHOP.enfinity/WFS/CDS-CDS_SMI-Site/en_US/-/USD/ViewProductDetail-Start?ProductRef=Sol10-U8-SP-x86-FULL-DVD-G-F@CDS-CDS_SMI

- the first open usually work; click the browser's "refresh page" button

- every second reload of the download page the browser hangs
  (un-freeze by killing the java subprocess that is started by firefox-bin)