I have an extension that has been signed by Mozilla that shows up as "could not be verified for use in Firefox. Proceed with caution" in the add-ons manager. I installed the extension by copying the file to ~/Library/Application Support/<vendor>/Extensions/{id}/@name.xpi on OSX and to %appdata%\Mozilla\Extensions\{id}\@name.xpi on Windows. Upon restart of Firefox 42 the extension gets installed and works fine, except for the worrying message. However, when I install the extension by dragging it onto the Firefox window it gets installed fine and does NOT show the worrying message. Is this a bug in Firefox or am I installing my extension incorrectly and is the documentation at https://developer.mozilla.org/en-US/Add-ons/Installing_extensions incomplete?