Callbacks directory has wrong permissions
After installing the Debian package for RT 3.0.11 and RTIR version 1.0.5 (?), we found that the directory /usr/share/request-tracker3/html/Callbacks was not readable by the Apache WEB server, and so the RTIR extensions (especially, the RTIR menu in the main navigation bar) did not appear.
Doing a 'chmod -r 755 /usr/share/request-tracker3/html/Callbacks' fixed the problem.
This has been reported to BestPractical who have promised to fix this in version 1.2 of RTIR.