If you have Windows, go to <strong>Start</strong> | <strong><u>H</u>elp</strong>. Then, under the <strong><u>C</u>ontents</strong> tab, go to the topic <strong>Introducing Windows 95/98</strong> | <strong>How to Use Help</strong> | <strong>Get more out of help</strong>, and click on the word "frame". In Windows 98, it should look something like <a href="http://www.1ec5.org/mingerweb/img/popup-def01.bmp">this</a>.
This could be useful for Mozilla Help (if anyone even uses it), and for "What's This" help in the Preferences dialog and various managers. I'm thinking it could be useful because Mozilla often has lots of jargon in its interface.
What do you think? (And if this can already be achieved, please correct me.)