This is not for Stellarmate OS, but for Ubuntu Mate 20.04.1 LTS (Focal Fossa) 64bit, but maybe helps to someone.
The reason why on this system the execution of start.sh fails with No such file or directory is simple:
Firecapture v2.6 is a 32bit application and by default it is not allowed to execute on 64bit OS.
To enable Firecapture v2.6 on 64bit Ubuntu Mate we need to run following from command line:
sudo dpkg --add-architecture armhf
sudo apt-get update
sudo apt-get install libc6:armhf libncurses5:armhf libstdc++6:armhf libxext6:armhf libxrender1:armhf libxtst6:armhf