you have (or your distro has) installed the widevine drm plugins for firefox (or whatever browser) that are included by default on windows and mac os. these are

you have (or your distro has) installed the widevine drm plugins for firefox (or whatever browser) that are included by default on windows and mac os. these are proprietary plugins, but some convenience-oriented distros distros include them because many users expect them. some linux users are on linux because they want to eliminate proprietary software from their computer altogether. which means no access to un-broken drm media.