Vitali, I don't see any problem with your project. What I did:
1. Unziped https://rapidshare.com/files/271188828/stopka-ui-test.zip
2. Imported it as an existing project.
3. Enabled JBoss Tools Knowledge Base: Project Properties for stopka-ui-test -> JBoss Tools Knowledge Base
4. Opened src/main/webapp/test.jspx
5. Ctrl+Clicked on "file" in line 11: <stopka:css file
6. stopka.tld is opened.