how to install JIRA add-ons for applications operating behind a firewall and disconnected from the Internet?

[Nic Brough -Adaptavist-]

Find a machine that can connect to the internet, go to the marketplace and look for each add-on's "install" link which will let you download the .jar or .obr file.  Move those (if necessary) onto a machine that can connect to your JIRA system, log in as an admin, go to plugin management and click "upload addon".  Then upload the files you downloaded earlier