What a trade-off decision to make.
Go to a backlevel Firefox in order to have an unsigned version of Ghostery and AdBlockPlus that I've been using.
Or keep an uplevel Firefox without these useful extensions and hope developers will update to signed versions soon.
It looks like Firefox disabled the unsigned addons with good security justification: to enable introspection of plug-in code to make sure it isn't doing something bad.
Anon is feeling a bit hosed. Fuck.