FireFox on Mac OS re-formats the window constantly when not using maximized view

On Mac OS, while using FireFox browser, only in UCI, the window re-formats itself constantly while not maximized. This seems like a bug and there is no known fix except using another browser or maximized view. Generally, this is not supported - FireFox is not supported for Mac OS. Please, address this as many users and customers prefer to use FireFox instead of another browser.