OS - Solaris Sparc, Solaris x86
Browser - Mozilla 1.2.1, NS 7.0, NS 4.76

Steps to reproduce -

1) Install j2sdk1.5.0 on the target machine.
2) Register Plugin with the browser and invoke the browser.
3) Run the following demos bundled with the jdk, under -

{jdk_installed_dir}/demo/plugin/applets/MoleculeViewer/example3.html
and
{jdk_installed_dir}/demo/plugin/applets/SortDemo/example1.html

4) The applets load fine but when the user tries to go back to the previous page after the applet loads, the browser hangs.
All the other demos do not have this problem.

Note - These two demos work fine on Linux and windows. Tried on Redhat Advanced Server 3.0 and Sun Desktop Mercury with Mozilla and did not see the hang.