1) Install FireFox 2.0.0.3 with AdBlock plus plugin
2) hit http://bbs.darktech.org/test2.html
3) Browser will hang

or just access the testcase mozilla folks provided:

http://bugzilla.mozilla.org/attachment.cgi?id=260034

Problem can be reproduced with the 1.6 JRE, but NOT the 1.5 JRE.

when it hang, breaking in the debugger given this stack:

#0 0x00a127a2 in _dl_sysinfo_int80 () from /lib/ld-linux.so.2
#1 0xb7cc3404 in poll () from /lib/tls/libc.so.6
#2 0xb27abb18 in JavaVM5::ProcessWorkQueue ()
   from /usr/java/jre1.6.0_01/lib/i386/libjavaplugin_nscp.so
#3 0xb27acf1d in JavaVM5::GetJavaObjectForInstance ()
   from /usr/java/jre1.6.0_01/lib/i386/libjavaplugin_nscp.so
#4 0xb27a77d4 in JavaPluginFactory5::GetJavaObjectForInstance ()
   from /usr/java/jre1.6.0_01/lib/i386/libjavaplugin_nscp.so
#5 0xb27a9de0 in JavaPluginInstance5::GetJavaObject ()
   from /usr/java/jre1.6.0_01/lib/i386/libjavaplugin_nscp.so
#6 0xb2809e5f in CNSAdapter_JavaPlugin::GetJavaObject ()
   from /usr/java/jre1.6.0_01/plugin/i386/ns7/libjavaplugin_oji.so
#7 0xb58634cc in nsHTMLAppletElementSH::GetPluginJSObject (this=0x8d73998,
    cx=0x8a6fd60, obj=0x8d7b180, plugin_inst=0x8d46c28, plugin_obj=0xbfffc5ac,
    plugin_proto=0xbfffc5a8) at
../../../../mozilla/dom/src/base/nsDOMClassInfo.cpp:9116
#8 0xb5862d38 in nsHTMLExternalObjSH::PostCreate (this=0x8d73998,
wrapper=0x8d72718,
    cx=0x8a6fd60, obj=0x8d7b180)
    at ../../../../mozilla/dom/src/base/nsDOMClassInfo.cpp:8867
#9 0xb5438565 in nsObjectFrame::NotifyContentObjectWrapper (this=0xaf25e02c)
    at ../../../mozilla/layout/generic/nsObjectFrame.cpp:2173

So this is a hang inside the plug-in itself.

The only reason the adblock thing is relevant here is a timing
issue -- the JSobject wrapper for the object exists before the
plugin is instantiated. You could get the same result without
adblock by having the <object> start out as display:none, and
then from script toggling its display to "inline". That should
hang as well, even if adblock is not installed. Again, the key
is that we ask the plug-in for its JSObject, and it hangs instead
of returning one... and that's not something we can fix in the
browser.
 
Testcase that doesn't need adblock This hangs both trunk and
branch, whether adblock is installed or not, as expected.