Looks like this was intentional, to save some maintenance overhead, since alternatives exist: https://bugzilla.mozilla.org/show_bug.cgi?id=1907034
Firefox
A place to discuss the news and latest developments on the open-source browser Firefox
Well that sucks.
I wouldn't have even been doing that if I could add custom "home" buttons to the toolbar.
A custom home button?
You can set a custom URL for your homepage and there is a "homepage" button you can add to your toolbar.
It would be nice to have a button that you can set to open a URL of your choice.
you can do that, basically you make a bookmark that leads to the desired url, and give it a blank title, and save it to the bookmarks toolbar, now if its the only item in the bookmarks toolbar now you bookmark toolbar has one icon in it with no text, then use the customize toolbar feature to move the bookmarks toolbar to the desired location, and voila! Custom homepage button