Problem is originally reported on bugzilla.mozilla.org with "critical" severity. (https://bugzilla.mozilla.org/show_bug.cgi?id=189485).
Many customers are affected by this including Yahoo! and Klocwork.
The problem causes browser to either crashes or hangs. During hang condition, if browser window is killed, FF ghost process still gets left behind.
Couln't make 6u4 last build.
Retarget to 6u5 b5
Problem root cause:
Java Plugin crashes during page loading because it fails to scan a malformed <object> tag.
The same page however is able to load fine with IE.
Will try to get fix in to 6u4 b4