Looks like:

option/alt + Home

should do the trick.

Note: If the help article doesn't detect that you use a Mac, there's a selector on the right side of the page to switch it to Mac OS: Keyboard shortcuts - Perform common Firefox tasks quickly.

I see that but there is no "home" key on a small magic keyboard.

Oh, I'm not familiar with that keyboard, sorry.

(I looked at a picture of it, but there's no obvious Fn or Command combination for Home in the image.)

I think that Home would be "fn-left arrow", so try Option and "fn-left arrow.

• /questions/1326327 Change the homepage hotkey.