A: YouTube will work in basic HTML5 mode (480p/720p). Netflix will likely fail because Widevine DRM on Firefox 78 is too old to validate current licenses.
While this setup is not recommended for primary, secure daily driving, it is the best possible modern browsing experience available for your legacy hardware. Keep your expectations realistic, use a robust ad-blocker, and consider upgrading your machine at the earliest opportunity.
Note: You can replace en-US with your local language code (e.g., fr , de , ja , zh-CN ). Look for the file named: Firefox 78.15.0esr.dmg