This message was reported to full-disclosure
It is possible to crash firefox with a few lines of HTML.
This issue is being watched upstream by these bugs
The Mozilla Software Foundation do not in general treat simple
unexploitable crashes of a browser as a security issues. Removing
Fedora Core 3 is now maintained by the Fedora Legacy project for security
updates only. If this problem is a security issue, please reopen and
reassign to the Fedora Legacy product. If it is not a security issue and
hasn't been resolved in the current FC5 updates or in the FC6 test
release, reopen and change the version to match.
Looks like this got fixed already by upstream.