Qhn, I think you miss understood me. Sites can have code designs (layouts/ASP/.Net) structures that they use to enhance the site and gear it towards a particular browser. Some companies that use group policies to lock their people into say interenet explorer may ask their coders to say, force a .net structure and lock in system called routines. Trying to view the site from anything else except IE will cause certain controls not to display or self authentication not to occur.
If you have ever used Outlook Web Access (OWA) you will find that it use to display differently in Firefox/Safari than when you used Internet Explorer. Java for example will through a Data Exception Protection error (DEP) if the wrong version is being used and a system call is being made. Microsoft Virtual Java Machine Support is not the same thing as Java SE version 14 or 16. If you are say using Java SE 6 without any of the release updates you would be running a java code that doesn't have the latest call packages or support for the garbage collection routines.
Flash uses addon calls to identify itself to Microsoft and allow controls such as keyboard interactions and on screen controls to be made. If this is set for a specific version use calls made that may be interpretted differently from compatability view and strait ie8http://social.answers.microsoft.com/Forums/en-US/InternetExplorer/thread/68259a6d-e5b2-46c4-86e2-080412379e6a