A heavily patched extension manager has been introduced this release by Mike Hommey. It is designed to work around the deficiencies in the upstream's current offering. Unfortunately, the registration process for extension and locale packages has now changed in an incompatible way. The packages will install correctly but won't actually be registered with Firefox. Maintainers are aware of the issue and are working on new packages that will work with this new mechanism. Please do not file bugs on this issue.