Offer your visitors a choice. Java can be slow and the older browsers do not have the capability to read it. Avoid using pop up boxes asking for your visitor's name, etc. They are unprofessional and can be irritating to your visitors when they're trying to view your site. It disturbs my concentration.
All web browsers are different.
View your site through different browsers so you can see how your visitors will view your site. Just because you have the newest version - don't mean everyone does. Frequently update the content on your site. Make your content valuable and informative for your visitors - you want them to keep coming back.