Install the Extension

From PluginWiki

If you're trying to install the plugin you may find that your browser instead opens it up as though it were a ZIP file. You'll see something like this:

Or your browser may say it doesn't know what to do with this kind of file, and ask you about opening it.

If either of these happen, then save the file and install it manually as described in Private Releases. You'll get automatic updates from then on, so you'll only need to do this on your first install.