This extension exchanges personal data (current website and manifest URLs, as well as other PWA details) with the native program when the user initiates the PWA installation. This is necessary in order to correctly obtain and parse the Web Application Manifest and install the PWA. Data are stored on the computer as long as that PWA is installed. No personal data leave the computer or are sent to third parties.
As installed PWAs are running inside a Mozilla Firefox browser, you also need to agree to the Firefox Privacy Notice.