This plugin allows you to send requests directly to your browser and perform a custom search. Some examples: http://www.google.it/search?q= if you want to perform a search on Google or http://bugs.debian.org if something is wrong with your system (assuming your distribution is Debian).
First add the plugin to your panel. Then you can go to the config dialog and enter the base URL you want to use for search queries (see th examples above).
Once it's done, you can just to type in some keywords and press
ENTER and the plugin will open your web browser and perform the search on the URL you've specified.
Bugs should be reported to the Xfce bug tracking system.
The normal (and best) way to get this plugin is to use the package manager or port system of your operating system.
If it isn't available there, or if you want a different version, you can download it in source form from http://archive.xfce.org/src/panel-plugins/xfce4-smartbookmark-plugin/.