Firefox's titlebar uncheck not working.
If you use KDE you can force removal of it using KDE's window rules. If you already have a custom window rule in place for Firefox, perhaps it is overriding Firefox's inbuilt setting?
I think this is due to this setting in the browser settings
browser.tabs.drawInTitlebar=false # Use client side decoration
Try turning it off via about:config in the firefox address bar, then searching for the setting. set it to true and restart firefox.
There are two scripts available, but using these scripts maximizing is also removes minimize,maximize and close buttons.
Yes it would, but you could click on the programs icon in your tray and select maximize/minimize there.