Installing firefly on a raspberry can be done with a LAMP stack, but to have less configuration to worry about, I use docker. This is a bit tricker than 'normal', as raspberry uses the ARM architecture. Luckily, most official images are ready for this. We do need to install docker and docker-compose.
The OS I was running when writing this was Raspbian Stretch Lite (Version:November 2018)
This is the easy part. Long story short: I'm a trusting fellow and I use the installscript provided by docker:
curl -fsSL get.docker.com -o get-docker.sh && sh get-docker.sh