Those keyboard shortcuts are not included in Firefox because your operating system already has those built-in. To change between windows of the same app on a Mac, the keyboard shortcut is Command + ` (tilde). The tilde key is the button on the left side of the 1 key on a standard keyboard. Macbooks also offer a trackpad gesture to change the active window. Swiping up on the trackpad using three fingers should allow you to change the window. I find the [https://www.idownloadblog.com/2019/06/27/switch-between-windows-on-mac/ How to quickly switch between windows and apps on Mac] page has a lot of information about the functionality you are looking for. Hope this helps.

D'oh! Thanks, Wesley.