One cool new thing you can do with search plugins in Firefox 2 is support “search suggestions.” The idea is that as the user types in the search bar, search plugins that support this feature can query the server for possible completions for whatever the user is typing, which allows Firefox to display possible search terms in a popup that appears under the search bar.
If you have a Firefox 2 build, try this using the Google or Yahoo search engine. If you pause while typing the search term, a list will appear suggesting possible completions for the term.
This is very cool. And now I’ve just posted an article explaining how to implement support for this feature. Let me know if anything doesn’t make any sense!