Behavior of Modal dialog on windows and solaris/linux differ. On windows modal dialog poped up by an applet running in the browser blocks applet AND browser (user can not push "Back", "Forward", etc buttons in the browser). While on solaris/linux, modal dialog poped up by an applet is modal to java process only, not to Netscape process.
There is a ModalityListener.java implemented for windows. Files that were modified/added in awt to solve this problem on windows:
src/win32/classes/sun/awt/windows/ModalityListener.java
src/win32/classes/sun/awt/windows/ModalityEvent.java
src/win32/classes/sun/awt/windows/WToolkit.java
These are the fixes needed for plug-in to block the browser window when applet pops up a modal dialog.
Same type of functionality is needed for Solaris/linux, so that plug-in could implement a fix to block Netscape browser as well as java. See bug 4414115