Notes to myself because I keep forgetting. tl;dr Unzip it into the /opt/ directory. I want to install Filezilla - so I can SFTP files around. Sadly, the Flatpak version is unmaintained and the version in apt is out of date. Luckily, you can download the zipped version. Their Wiki helpfully says: If you have special needs, don't have sufficient rights to install programs or don't like…