Manually switching Java versions of the Java Plug-in

• Enter about:config in the Firefox or SeaMonkey Location Bar, find the preference plugin.scan.SunJRE and modify its value to 1.6 (for example). 

http://kb.mozillazine.org/Java#.22Java_Plug-in_for_Netscape_Navigator_should_not_be_used_in_Microsoft_Internet_Explorer.22