I've now had a chance to try this script, having been away from home for the last few days, and it loads in my OrangeMonkey extension fine but doesn't actually seem to do anything on Facebook other than add a 'previous' and 'next' button at the bottom right of the page.
The buttons don't seem to do anything, and there is no apparent change in the behaviour of the page.
I can't see anything obviously wrong with the code, but I know nothing about writing scripts!