Addon installation error -203

Ok - I downloaded new version of Fire fox. Posiibly closssed before complete. Did have 3 addons but seem to have gone. Tried to add then in again & tried others but near end of install get error: the http// for the addon with _statusbar -0.9.6.3-fx.xpi then text unexpected installation error; review error consol log ; -203.

Any ideas what I need to do. I've uninstalled Firefox & reinstalled still get problem

Rob