Thanks for sharing your solution! Not sure what is causing it (maybe it's OpenSSL binding related), and am currently not really targeting FreeBSD yet.
I wasn't fully ready with this tool for the Firefox Send release to be honest, would have loved to be able to provide better binaries and packages for more platforms, which are a work in progress.
If you believe you can improve the README with your solution, be sure to submit a [PR](https://gitlab.com/timvisee/ffsend/).
Happy to see it's working! :)