JBIDE-4877 it's not the same acctually.
That issue is about code completion for components w/o prefix but the corresponding namespace should be defined.
For example:
if you have xmlns:a4j="http://richfaces.org/a4j defined for the page and start typing <command| then code assist should suggest <a4j:commandButton

What are current options when using JBoss Tools?

• modify Facelets file templates for creating new files and list all favorite namespaces there
• use autocompletion of detected namespaces (write xmlns:xyz="..." and autocompletion will offer you available namespaces)
  But both of the solutions are not as straight-forward as it could be.

There is one more option.
You can DnD a tag from Palette View and the namespace will be inserted automatically.

Ok. Let's describe again what we expect to see when this feature is done:

The information about the prefixes could be retrieved from:
faces-config.xml generated by RichFaces CDK: faces-config/faces-config-extension/cdk:prefix
scanning the Facelets (XHTML) files in a project and collecting used namespace prefixes (xmlns:*)

JBT has the list of all the libs available for the project (jars, resources... within the classpath). So we can use all the URI from that list.