Comment 17 for bug 709103

There seems to be another change in the way extensions work in Firefox 4. Before version 4, extensions used to be automatically unpacked to a directory on restart if you put the .xpi in the extensions folder. Now they don't have to be - the .xpi on its own is sufficient. Unless the extension contain binary components, like this one. A new <en:unpack>true</em:unpack> needs to be added to the install.rdf file for this to be done, but it only appears to be done on installation through Firefox (not if you just copy it to the directory)

Hopefully, the enclosed patch will work. make local-install should install it as an unpacked directory rather than an .xpi to the extensions folder. (Presumably it would conflict with an .xpi of the same extension already there, though, so that may need to be manually deleted if it exists)