You can search the Library much like you would any other search engine. Results will be limited to those extensions which match every search term you give.
In addition to general keyword searches, you can search for extensions which match particular information through using these tags:
title:glulx title:"glulx text effects"
author:emily author:"Emily Short"
These tagged terms can be combined with each other and with regular terms:
title:vorple images title:glulx author:emily