Installation is supported on all modern desktop and mobile devices. Whether the PWA can be installed by the browser on the operating system differs by browser/operating system combination. Most browsers support installing PWAs on all operating systems—Chrome OS, MacOS, Windows, Android, Linux, etc.—directly or when an extension is installed.
Apple is unique when it comes to PWAs: PWAs can be installed on macOS from any browser except Safari. The opposite is true for iOS versions before 16.4, where PWAs could only be installed in Safari. PWAs can be installed on iOS/iPadOS 16.4 or later from any supporting browser.
Apparently, it’s not an official extension by Mozilla either, but published by a third party.