Just updated to 0.9.10 and noticed that some of my scripts weren't
working. So I looked in Tools > Add-ons > User scripts and only 3 of
them were listed! :-(
The listed scripts were actually the first 3 entries in config.xml, so
I tried deleting the 4th script in config.xml, and that managed to fix
the problem.
I'm not sure what was causing it (some kind of parsing bug at a
guess?) but it was rather disconcerting. If it's any help, this was
the script causing the problem:
http://userscripts.org/scripts/version/25105/362615.user.js