Are you referring to the section on page 29, entering commands into a Terminal prompt? Ensure you type the commands exactly as shown!
When you type ./firefox-bin –profilemanager, there should be a single space followed by a dash and immediately afterwards profilemanager. It sounds like your Mac is just running the Firefox program (or binary file / executable), and not seeing the -profilemanager part.
What happens if you type about:profile directly into a Firefox browser window?
Can you email screenshots directly to our support email address email@example.com and I will take a look.
In the meantime, may I suggest Waterfox. This is available from https://www.waterfox.net/releases/ in both Mac and PC versions, and requires no additional add-on installation or profile management. It should run aside your existing Firefox installation.
Let me know how you get on / send screenshots of your existing Firefox issue with the Terminal command to start the Firefox profile manager.