In the upcoming release of Firefox 49, Mozilla will include support for Google's Content Decryption Module (CDM), Widevine. With this support, Firefox users on Linux will finally be able to watch Netflix content; previously Linux users had to watch Netflix using Google's Chrome browser.
Mozilla Firefox users on Windows and Mac already had the ability to watch Netflix content as Widevine was switched on earlier for those users. Firefox 49 brings the Linux version up to parity.
While it will be technically possible for Firefox for Linux users to play Netflix content, Ghacks warns that:
“Support depends on the services as well though, and it is possible that Linux users won't be able to stream videos on Netflix or Amazon Video right after the release of Firefox 49. This should work however by manipulating the user agent of the browser to Chrome for the time being.”
CDMs, such as Widevine, is required to play DRM-protected HTML5 audio and video. Due to the easiness of ripping HTML5 content from browsers to a local machine, many providers have opted to wrap their content in a protective layer of DRM. Users will be able to disable Widevine support from Firefox too by setting it to never activate. Many anti-DRM folks will be running Firefox on Linux and will probably want the ability to disable this functionality.