If you go into the Firefox settings in the '''Content''' tab, there should be a '''Play DRM content''' checkbox that allows you to enable DRM on Firefox. Admittedly, I'm not sure if it will still work properly for you, given that you are on a very old version of Firefox because you are still on Windows Vista. I'm not sure if the Google Widevine software still installs properly automatically on that version of Firefox. You may need to press the menu button in Firefox, select '''Add-ons''' and then select '''Plugins''' from the left side to manually enable Google Widevine in the list of plugins. Hope this helps.