Non XyWrite but we all run a browser or two.
In addition to Kari's recent post
I run Mozilla "Nightly" which is updated everyday
https://nightly.mozilla.org/ it's currently Version 43.0a1
(2015-08-22)
Recently the new signed addons "feature" was introduced which
disabled all unsigned addons not downloaded direct from Mozilla
Very soon all Firefox users will face their addons being blocked
from running unless signed directly from Mozilla
To fix this
In
about:config search for "signatures" and make it FALSE
(double click "true") All your addons will happily return (for now)
xpinstall.signatures.required;false was true on 2015 Aug 12