While we currently don't have an FFR client developed for macOS, we could get the Windows version to run on Macs. To do so, you'd have to install Wine, which is software that can run Windows programs on other operating systems, including macOS.
1. Go to
https://dl.winehq.org/wine-builds/macosx/download.html and click on the option that says 'Installer for "Wine Stable"'. A file should be downloaded.
2. Double-click on the downloaded file (should have a '.pkg' extension), and the macOS installer program should open. Follow the instructions shown.
3. For your case, it doesn't matter whether you choose to install the package for all users or for your current user. Either choice is fine.
4. When the installation is done, you should see an entry that says "Wine Stable" in your Launchpad.
5. Click on the entry, and a new Terminal window should open, which gives a short introduction on some important wine commands.
6. Close the Terminal window.
7. Download the FFR Windows client from
https://www.flashflashrevolution.com/download/ if you haven't done so yet.
8. Extract the downloaded archive.
9. Navigate into the folder and double-click on the file that says either 'R3' or 'R3.exe'. The game should run.
Feel free to tell us if you've encountered a problem getting the game running.