Answer by coobird for How to deploy a java applet for today's browsers (applet, embed, object)?

Answer by coobird for How to deploy a java applet for today's browsers (applet, embed, object)?:
There is a section in The Java Tutorials titled Using applet, object and embed Tags which addresses the issue.

From the General Considerations:

Deploying Applets on the Internet Versus an Intranet

When deploying applets:

• Use the applet tag if the Web
  page is accessed through the Internet.
• Use the object or embed tag if the Web page is accessed through an
  Intranet.

Deploying Applets for Specific
Browsers

When deploying applets:

• For Internet Explorer only, use the
  object tag.
• For the Mozilla
  family of browsers only, use the
  embed tag.

If you must deploy an applet in a mixed-browser environment, follow the guidelines in the section Deploying Applets in a Mixed-Browser Environment.

It should be noted that the applet tag has been deprecated, so it's probably not desirable to use that tag. (More information on the applet tag from the W3C)

(Note: Links have been updated from the previous edit to link to The Java Tutorials.)